Đề ôn thi Đề thi vào lớp 10 Trường THPT Chuyên KHXH môn Tiếng Anh - Mã đề KHXH-31

At first glance, a screw seems incredibly simple. It is a common type of (35) __________ used to fasten materials like wood or metal together. Its main job is to hold objects securely, performing this task with remarkable efficiency. While it looks like just a nail with grooves, its design is based on the inclined plane, a fundamental engineering principle.

Imagine a ramp, or inclined plane, wrapped around a central cylinder. This helical structure is known as a thread, and it is a (36) __________ feature of any screw. The distance between each turn of the thread is called the "pitch." This winding path is key to how the screw functions as a powerful simple machine.

The genius of the screw is how it converts one motion into another. When you turn a screw, you apply rotational force. Thanks to its design, you (37) __________ apply a huge amount of pushing force directly. The screw changes this easy turning into a powerful, straight-line push. (38) __________ allows it to enter hard materials like wood.

The threads create significant friction, helping to hold the screw firmly in place. The finer the threads, (39) __________ the grip it provides. (40) __________ simple design hide such a clever physics principle. This mechanical advantage makes the screw a strong and reliable fastener, much more secure than a nail.

Screws are essential; they (41) __________ a vital role in everything from constructing furniture to assembling electronics. (42) __________, the humble screw is a perfect example of engineering genius, transforming a small rotational effort into a powerful fastening force.

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.