Đề ôn thi Đề thi vào lớp 10 Trường THPT Chuyên KHXH môn Tiếng Anh - Mã đề KHXH-61

Blood is an (35) __________ fluid that circulates throughout our bodies, delivering necessary substances like nutrients and oxygen to tissues. It is a complex mixture, but two of the most important components are red blood cells and white blood cells. Each type has a unique and vital mission to perform.

Red blood cells, also known as erythrocytes, have a very specific job. They are (36) __________ for transporting oxygen from the lungs to the rest of the body. This critical task is possible because they contain a special protein called hemoglobin, (37) __________ gives them their characteristic red color. In terms of numbers, there are (38) __________ more red blood cells than any other type of cell, making up about 45% of the blood's total volume.

White blood cells, or leukocytes, have a completely different purpose. Their primary role is to protect the body against illness and disease. As key players in the immune system, they actively (39) __________ infection by attacking bacteria, viruses, and other harmful invaders. Unlike red blood cells, they do not contain hemoglobin, are generally larger in size, and have a nucleus.

The differences between these two cell types are significant. Red blood cells focus on oxygen delivery and are incredibly numerous. (40) __________, white blood cells act as the body's defenders and are much fewer in number. A healthy body maintains a careful balance between them, and a major change in this ratio can (41) __________ a person's overall health.

In conclusion, even though their functions are distinct, both red and white blood cells (42) __________ a crucial role in keeping us healthy. They are teammates in the circulatory system, and understanding their different jobs helps us appreciate the amazing and complex way our bodies operate to sustain life.

Have you ever stood on a balcony in a bustling city like Ho Chi Minh City at night, looked up, and tried to find the stars? Chances are, you saw very few, if any at all. This phenomenon, often called 'sky glow,' is a direct result of light pollution, a growing environmental concern in urban areas worldwide. It is more than just an inconvenience for amateur astronomers; it is a problem with significant consequences for our environment, wildlife, and even our own health.

The primary cause of light pollution is the inefficient and excessive use of artificial light. In rapidly developing cities, sources are everywhere: streetlights that shine in all directions instead of just downwards, dazzling advertising billboards that stay on all night, and office buildings like the Bitexco Financial Tower that illuminate the sky. This poorly directed light scatters in the atmosphere, creating a bright haze that blankets the city and obscures the natural darkness of the night sky.

The ecological impact is perhaps the most alarming. Many animals rely on the natural cycles of day and night to navigate, hunt, and reproduce. For example, newly hatched sea turtles are genetically programmed to find the ocean by moving towards the brightest horizon, which should be the moonlit sea. Instead, they are often fatally lured towards bright city lights. Similarly, migratory birds become disoriented by illuminated skyscrapers, leading to exhaustion and collisions. Even smaller creatures like insects, crucial for pollination, are affected, as many of them are nocturnal.

Beyond its effect on wildlife, light pollution has direct consequences for humans. Our bodies are tuned to a natural circadian rhythm—our internal 'body clock'—which is regulated by light and darkness. Constant exposure to artificial light at night, especially blue light from LEDs, can disrupt this rhythm, leading to sleep disorders and other health issues. Furthermore, it represents a significant waste of energy and money. Every photon of light that shines uselessly into the sky is wasted electricity, contributing to unnecessary carbon emissions and financial cost.

Fortunately, light pollution is a problem with achievable solutions. Simple changes can make a huge difference. These include using fully shielded light fixtures that direct light downwards, installing motion sensors so lights are only on when needed, and simply turning off unnecessary lights. Raising public awareness is also key, encouraging communities and policymakers to adopt smarter lighting practices. By making our cities darker, we can bring back the stars, protect wildlife, and create a healthier, more sustainable urban environment.