Đề ôn thi Đề thi vào lớp 10 Trường THPT Chuyên KHXH môn Tiếng Anh - Mã đề KHXH-170

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.

Have you ever experienced something strange? You and a friend are discussing a new brand of sneakers, and just a few hours later, an advertisement for those exact shoes appears on your Instagram or Facebook feed. It can feel like your smartphone is secretly listening to your conversations. While that’s a common fear, the reality is a bit more complex, and it has everything to do with the digital footprints we leave behind every time we go online.

The truth is, your phone probably isn't listening. Instead, tech companies use highly sophisticated data tracking methods that are much more effective. When you browse the internet, small files called 'cookies' are stored on your device, tracking the websites you visit. If you search for a flight to Da Nang on the Bamboo Airways website, that information is recorded. Later, when you are scrolling through social media, the system recognizes your interest and shows you ads for that airline. This interconnected web of data sharing between search engines, social media platforms, and online shops is what makes the ads seem so magically relevant.

Every 'like', share, search query, and even how long you look at a picture contributes to building a detailed digital profile of you. This profile doesn't necessarily have your name on it, but it contains your interests, age range, location, and shopping habits. This information is incredibly valuable. Advertisers pay tech companies to show their ads to specific profiles. They aren't buying your identity; they are buying access to a category of user, like 'a 15-year-old in Ho Chi Minh City who is interested in K-pop and bubble tea.'

This system of targeted advertising has both benefits and drawbacks. On one hand, it can be helpful. You might discover a new product or service that you genuinely need or find a great deal on an item you were already considering. The ads are more relevant to your life than random commercials. On the other hand, there are significant privacy concerns. Many people feel uncomfortable knowing their online behavior is being constantly monitored and analyzed. It can also create an 'echo chamber', where you are only shown things that fit your existing preferences, limiting your exposure to new ideas.

Ultimately, understanding the basics of how targeted advertising works makes you a more informed digital citizen. While these systems are a core part of how many 'free' online services make money, you are not powerless. You can take steps to protect your privacy by managing cookie settings in your browser and checking the privacy permissions for the apps on your phone. Being aware is the first step towards having a safer and more conscious online experience.