根据短文内容，完成表格，每空不超过三个词。

We sometimes say the lion is “the king of the jungle” because it is stronger and more dangerous than the other animals. Most other animals in the jungle run more slowly than the lion, so it can hunt better. The lion is the top animal in the land food chain.

In the sea, the shark is at the top of the food chain. Most other sea animals swim much more slowly than it. It can also use its big teeth to catch other sea animals and eat them.

What is at the top of the world's food chain? Humans are! We are not the biggest or fastest, but we are the cleverest! We could not catch up with most animals, so we invented cars and now we can move the fastest. We could not fight better than a lion, so we invented guns. Now we can hunt the best.

People’s inventions help a lot, but they can be dangerous, too. For example, many years ago in Inner Mongolia, people used guns to kill a lot of wild wolves.

The wild wolves usually eat wild rabbits. But in recent years, the number of wild rabbits is becoming bigger and bigger because the number of wild wolves is getting smaller and smaller.

The wild rabbits competed for the grass with the sheep and cows. Much of the grassland became desert because the rabbits destroyed (毁坏) it seriously.

Remember that we are a part of the food chain, we are in danger, too! If we protect animals, we are protecting ourselves. Luckily, people have paid much attention to such problems. We will do more things to keep the balance of ecosystem in the future.

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