Đề ôn thi Đề thi vào lớp 10 Trường Phổ thông Năng khiếu môn Tiếng Anh - Mã đề PTNK-87

Many think of quicksand as a deadly trap from movies, where a person sinks completely. However, the reality is less dramatic. Quicksand is not a special soil; it is ordinary sand saturated with water. Because of its properties, you cannot sink completely in it, no matter how much you struggle.

Normally, sand particles are packed together, creating friction that supports weight. When water saturates the sand, often from an underground source, it flows between the particles. This water greatly reduces the (21) __________ between the sand particles. The sand loses its ability to support weight and behaves more like a (22) __________.

The science behind why you float is related to density. Quicksand is a mixture of sand and water, making it much heavier than just water. In fact, your body is less (23) __________ than quicksand, so you will float. This means you will only sink to about your waist.

The real danger, therefore, is not sinking but becoming stuck. The dense mixture creates strong suction around your limbs. Not only does panicking make the situation worse, but it also wastes precious energy. Trying to pull a leg out quickly requires the same force needed to lift a small car.

If you are ever in quicksand, stay calm. Avoid sudden movements and (24) __________ your weight over a larger area by leaning back. Move your legs slowly to let water flow around them, reducing the suction. In conclusion, while quicksand is real, it is not the fatal trap movies show.

Imagine a new student disrupting your entire class. This mirrors what happens when an invasive alien species enters a new environment. These are plants or animals introduced, often accidentally, to a region where they don't naturally belong. Without their usual predators or environmental controls, they multiply rapidly, overwhelming native species. [I] A striking example, particularly relevant in Southeast Asia, is the Golden Apple Snail, an unwelcome visitor causing widespread concern in agricultural lands.

Originally from South America, the Golden Apple Snail (Pomacea canaliculata) arrived in Asia, including Vietnam, during the 1980s, initially for aquaculture. [II] It quickly escaped cultivation, establishing vast wild populations. These snails are incredibly prolific, laying distinctive bright pink egg clutches above the waterline, each containing hundreds of eggs. Their rapid reproduction and ability to consume vast vegetation allowed them to spread, dominating vital agricultural landscapes like rice paddies, where they quickly became a formidable problem. [III]

The Golden Apple Snail's impact on rice cultivation is devastating. Young rice seedlings, vulnerable in their early stages, are a favored food source for these voracious eaters. Swarms of snails can decimate entire fields overnight, forcing farmers to replant multiple times, significantly increasing costs and reducing yields. This burdens farmers reliant on rice for livelihood. Beyond crop damage, their presence also alters water quality and competes with native aquatic species, disrupting the paddy's delicate ecological balance. [IV]

Recognizing this severe agricultural threat, Vietnam's Plant Protection Department has implemented various control strategies. These include promoting integrated pest management, manual collection of snails and their egg masses, and careful use of molluscicides. Farmers are also educated on methods like proper water management and introducing natural predators. Despite these concerted efforts, the snail's resilience and high reproductive capacity make complete eradication extremely challenging, requiring ongoing vigilance and adaptive approaches.

The Golden Apple Snail's story powerfully reminds us of our world's interconnectedness. What seems like a small, introduced animal can create enormous problems, impacting the environment, human populations, and even the food we eat. For young people, this highlights environmental responsibility and the ripple effects of human actions. Protecting our ecosystems, even from minor disturbances, is crucial for ensuring sustainable food supplies and preserving nature for future generations.