Đề thi thử số 6 — Reading 40 câu

Sleep is one of the most fundamental biological needs of human beings, yet it is often the first thing people sacrifice when life gets busy. In modern society, where productivity is highly valued, many individuals view sleep as a luxury rather than a necessity. However, decades of scientific research have demonstrated that adequate sleep is essential for nearly every aspect of physical and mental health.

During sleep, the body undergoes a series of critical restorative processes. The immune system produces cytokines, proteins that help fight infection and inflammation. Growth hormones are released, which are vital for tissue repair and muscle development, particularly in children and adolescents. The cardiovascular system also benefits from sleep, as blood pressure drops during restful sleep, giving the heart and blood vessels a chance to recover from the demands of daily activity.

The brain, too, depends heavily on sleep to function properly. During the different stages of sleep, the brain consolidates memories, transferring information from short-term to long-term storage. This process is especially important for students and professionals who need to retain large amounts of information. Research conducted at Harvard University found that participants who slept after learning a new task performed 20 to 30 percent better on subsequent tests compared to those who stayed awake.

Sleep deprivation, on the other hand, has serious consequences. Even moderate sleep loss — getting six hours instead of the recommended seven to nine — can impair cognitive function, reduce reaction time, and increase the risk of accidents. Chronic sleep deprivation has been linked to a higher incidence of obesity, diabetes, heart disease, and depression. The World Health Organization has even classified night shift work as a probable carcinogen due to its disruption of natural sleep patterns.

Despite these well-documented risks, many people continue to underestimate the importance of sleep. Experts recommend establishing a consistent bedtime routine, avoiding screens for at least one hour before bed, and creating a dark, cool, and quiet sleeping environment. By prioritizing sleep, individuals can significantly improve their overall health, mood, and cognitive performance. In the words of sleep researcher Matthew Walker, "Sleep is the single most effective thing we can do to reset our brain and body health each day."

Tourism is one of the world's largest industries, contributing over 10 percent of global GDP and employing hundreds of millions of people. However, the rapid growth of tourism in recent decades has raised serious concerns about its environmental and social impact. In response, the concept of sustainable tourism has emerged as a framework for developing the industry in a way that meets the needs of the present without compromising the ability of future generations to enjoy the same destinations.

Sustainable tourism is built on three pillars: environmental protection, social responsibility, and economic viability. Environmentally, it seeks to minimize the carbon footprint of travel, reduce waste, and protect natural habitats and biodiversity. Socially, it aims to respect local cultures, involve communities in tourism planning, and ensure that the benefits of tourism are distributed fairly. Economically, it promotes long-term profitability for businesses while ensuring that tourism revenue supports local economies rather than being siphoned off by international corporations.

One of the most pressing issues in tourism today is overtourism — a phenomenon in which popular destinations become so overcrowded that the quality of life for residents deteriorates and the natural or cultural environment is damaged. Cities like Venice, Barcelona, and Dubrovnik have experienced severe overtourism, with residents protesting against the noise, pollution, and rising housing costs caused by millions of visitors each year. In response, some cities have introduced tourist taxes, visitor caps, and restrictions on short-term rental platforms like Airbnb.

Ecotourism represents one promising branch of sustainable tourism. Unlike conventional tourism, ecotourism focuses on visiting natural areas with the specific goal of learning about the environment and contributing to conservation efforts. Costa Rica is often cited as a model for ecotourism. The country has set aside over 25 percent of its land as protected areas and has developed a thriving tourism industry based on its rich biodiversity. Local communities benefit directly from ecotourism through employment as guides, accommodation providers, and artisans selling handmade goods.

Critics argue that sustainable tourism is difficult to implement on a large scale because it requires cooperation among governments, businesses, and tourists themselves. Others point out that the term is sometimes used as a marketing tool — a practice known as "greenwashing" — by companies that make superficial environmental claims without making meaningful changes. Nevertheless, as climate change accelerates and natural resources become scarcer, the transition to more sustainable forms of tourism is not just desirable but necessary. The challenge lies in finding practical solutions that balance the economic benefits of tourism with the urgent need to protect the planet and its communities.

In the past decade, a revolutionary technology called CRISPR-Cas9 has transformed the field of genetics, offering scientists an unprecedented ability to edit the DNA of living organisms with remarkable precision. CRISPR, which stands for Clustered Regularly Interspaced Short Palindromic Repeats, was originally discovered as a natural defense mechanism in bacteria, which use it to cut and destroy the DNA of invading viruses. Scientists Jennifer Doudna and Emmanuelle Charpentier recognized the potential of this system and adapted it into a powerful tool for genetic engineering, an achievement that earned them the Nobel Prize in Chemistry in 2020.

The applications of CRISPR in medicine are already showing extraordinary promise. Researchers have successfully used the technology to treat sickle cell disease, a painful and potentially life-threatening condition caused by a single genetic mutation. In clinical trials, patients who received CRISPR-based therapy showed significant improvement, with many becoming free of the severe pain episodes that had previously dominated their lives. Other medical applications under investigation include treatments for certain types of cancer, inherited blindness, and muscular dystrophy.

Beyond medicine, CRISPR has significant applications in agriculture. Scientists are developing gene-edited crops that are more resistant to drought, pests, and diseases, which could help address food security challenges as the global population continues to grow. Unlike traditional genetically modified organisms (GMOs), which involve inserting genes from different species, CRISPR-edited crops often involve small, precise changes to existing genes — a distinction that has led some regulatory bodies to treat them differently from conventional GMOs.

Despite its enormous potential, CRISPR raises profound ethical questions, particularly regarding its use in human embryos. In 2018, Chinese scientist He Jiankui shocked the world by announcing that he had created the first gene-edited babies — twin girls whose DNA he had modified to make them resistant to HIV. The scientific community widely condemned this experiment, arguing that the technology was not yet safe enough for use in human reproduction and that editing the germline — changes that would be passed down to future generations — crossed a fundamental ethical boundary. He Jiankui was subsequently sentenced to three years in prison.

The debate over gene editing reflects a broader tension between scientific progress and ethical responsibility. Supporters argue that CRISPR has the potential to eliminate genetic diseases and improve human health on a scale never before possible. Opponents warn that without strict regulation, the technology could be used to create genetic inequalities, with wealthy individuals able to enhance their children's intelligence, appearance, or athletic ability. As the technology continues to advance, the international community faces the difficult task of establishing guidelines that promote beneficial research while preventing misuse. The future of gene editing will depend not only on scientific breakthroughs but also on the wisdom with which society chooses to govern them.

Throughout human history, powerful civilizations have risen to great heights only to eventually decline and disappear. The patterns underlying the rise and fall of these societies have fascinated historians, archaeologists, and political scientists for centuries. While each civilization had its unique characteristics, scholars have identified several common factors that contributed to both their success and their ultimate downfall, offering valuable lessons for the modern world.

The rise of a civilization typically begins with geographic advantages. Access to fertile land, fresh water, and natural trade routes provides the foundation for agricultural surplus, which in turn supports population growth and the development of specialized labor. The ancient Egyptians, for example, built their civilization along the Nile River, whose annual floods deposited nutrient-rich silt on the surrounding plains, enabling the production of abundant crops. Similarly, Mesopotamia — often called the cradle of civilization — flourished between the Tigris and Euphrates rivers, where irrigation systems transformed arid land into productive farmland.

As civilizations grow, they develop increasingly complex political and social structures. The Roman Empire, which at its peak controlled much of Europe, North Africa, and the Middle East, exemplifies this process. Rome's success was built on a combination of military prowess, legal innovation, and engineering achievements such as aqueducts, roads, and public buildings. The Roman legal system, with its emphasis on written laws and citizens' rights, influenced legal traditions that persist to this day. However, the very complexity that made Rome powerful also made it vulnerable. Maintaining control over vast territories required enormous military expenditure, and political corruption gradually undermined the effectiveness of governance.

Environmental degradation has played a significant role in the collapse of several ancient civilizations. The Maya civilization of Central America, which developed sophisticated mathematics, astronomy, and architecture, experienced a dramatic decline around the ninth century. While scholars debate the exact causes, evidence suggests that prolonged drought, exacerbated by deforestation and soil erosion from intensive farming, severely reduced agricultural output. Unable to feed their populations, major Maya cities were abandoned, and the civilization fragmented into smaller, less powerful communities. The case of the Maya serves as a stark reminder that even advanced societies are not immune to environmental collapse.

The lessons drawn from ancient civilizations remain remarkably relevant today. Modern societies face many of the same challenges that contributed to the downfall of their predecessors: environmental degradation, resource depletion, political polarization, and economic inequality. The difference is that today these challenges operate on a global scale, with consequences that affect the entire planet rather than a single region. Historians argue that understanding the past is not merely an academic exercise but a practical necessity. By studying the mistakes of fallen civilizations, contemporary societies can develop strategies to avoid repeating them. As the philosopher George Santayana famously wrote, "Those who cannot remember the past are condemned to repeat it."