Đề ôn thi Đề thi vào lớp 10 Trường THPT Chuyên KHXH môn Tiếng Anh - Mã đề KHXH-99

Caves are fascinating natural formations found all over the world, but have you ever wondered how they are created? The most common type of cave is a solutional cave, formed in a specific kind of rock called limestone. The main force responsible for carving these underground wonders is simple water, but the process is anything but fast. This process can take (35) __________ thousands of years, patiently shaping the world beneath our feet.

The journey begins with rain. As raindrops fall through the atmosphere, they absorb carbon dioxide from the air. This has the (36) __________ of making the water slightly acidic, creating a weak version of carbonic acid. When this acidic rainwater lands, it seeps down (37) __________ the ground and into any small cracks or fissures present in the limestone bedrock. This is where the key chemical reaction begins.

Limestone is primarily made of a mineral called calcium carbonate, which reacts with acid. Over time, the limestone (38) __________ by the acidic water, creating small channels. As more water flows through these initial paths, it dissolves more and more rock. These channels grow (39) __________ larger, eventually forming the vast rooms and passages we see in caves. It's a testament to how a gentle force can have a huge impact over a long duration.

The process doesn't stop once the main cave is formed. Inside the cave, this mineral-rich water continues to (40) __________ from the ceiling. As the water is exposed to the air inside the cave, it releases some of its dissolved carbon dioxide. This makes it less acidic and unable to hold as much of the dissolved mineral. Each drop leaves behind a tiny mineral deposit, (41) __________ builds up over centuries to form beautiful, icicle-like structures called stalactites.

The formation of caves is an incredibly slow process, requiring a precise combination of rock, water, and time. (42) __________, the results are some of the most spectacular and mysterious natural wonders on Earth. From the initial raindrop to the magnificent stone formations, the creation of a cave is a perfect example of nature's slow and persistent artistry.

When you buy a cup of milk tea or iced coffee in Vietnam today, you'll likely notice something different. Many popular cafes have stopped using plastic straws, offering paper, bamboo, or metal ones instead. This shift isn't just happening here; it's part of a global movement against single-use plastics, encouraged by government policies like Directive No. 33/CT-TTg. But while saying 'no' to a plastic straw feels like a good deed, it raises an important question: are these small changes truly helping our planet, or are they more for show?

The campaign against plastic straws gained popularity because it addresses a visible and relatable problem. Horrifying images of sea turtles with straws stuck in their noses went viral, making millions of people aware of the dangers of plastic waste in our oceans. For environmental groups, the plastic straw is an ideal target. It is not an essential item for most people, making it an easy thing to give up. In this context, refusing a plastic straw has become a powerful, symbolic act, representing a person's commitment to environmental protection and raising awareness of the larger issue of plastic pollution.

However, critics argue that the intense focus on straws is a distraction from bigger environmental threats. Statistically, plastic straws make up a very small fraction of the total plastic waste in the ocean—less than 1%. A far more significant problem is abandoned fishing gear, such as nets and lines, which constitutes a much larger percentage of marine debris and is far more deadly to sea life. By concentrating so heavily on straws, we may be ignoring these more damaging sources of pollution and giving ourselves a false sense of accomplishment.

Furthermore, the alternatives to plastic straws are not without their own problems. Paper straws often become soft and unusable quickly, and if they are contaminated with liquid, they usually cannot be recycled. Reusable straws, like those made from metal or silicone, require water and energy to be cleaned after every use. Some studies even suggest that certain alternatives might have a larger carbon footprint to produce than the plastic straws they replace, considering the entire lifecycle from manufacturing to disposal.

Ultimately, the war on plastic straws is complicated. While it may not be the magic solution to cleaning our oceans, its greatest value might be in starting a global conversation. It has forced consumers and companies to think more critically about our throwaway culture. The small act of choosing a different straw can be a gateway to bigger, more impactful changes, but only if we recognize it as a first step, not a final destination in the journey toward a healthier planet.