题目内容：

    When early humans killed a mammoth, how did they keep the meat before they could eat it all? We don’t know; maybe they didn’t. But perhaps they preserved their mammoth steaks in salt. However, it is hard to know for sure. We do know for certain that by 3,000 years ago, the Babylonians, Egyptians, and Chinese were all experts at salting. They used salt to preserve food.

For thousands of years, salting was a common way to preserve food. But for a long time, no one knew why salt worked. Then, in the 1800s, a Frenchman named Louis Pasteur discovered the secret: bacteria. What does salt have to do with bacteria? First, bacteria need moisture to grow and multiply. Salt pulls moisture out of food, so the bacteria no longer have enough moisture. Besides, salt is poisonous to many bacteria. If you cover food with salt, bacteria outside the food die before they get in, and bacteria already in the food are poisoned by the salt.

So how do you preserve food with salt? For meat or fish, you pour on a layer of salt, then rub it in well. Hams are often made this way. Another way is to alternate layers of food and salt in a big container. The salt will draw the moisture out of the food, creating a brine  that the food sits in. You’ll need to make sure the brine completely covers the food; any food left exposed to the air will spoil. If you preserve cabbage this way, you’ll make sauerkraut.

How well salt preserves food depends on how much is used. The more salt, the longer the food is preserved. Unfortunately, using enough salt to preserve food for a very long time can cause problems. It can make food tough. It can destroy flavor. And, of course, it can make the food too salty to eat, which is harmful to our health.

Today, even though we no longer rely on salt to keep our food fresh, we haven’t lost our taste for salt. We don’t want to give up our bacon, salami, and watermelon pickles!

1.Why are examples of the ancient people mentioned in the first paragraph?

A.To make an introduction to the topic.

B.To explain our ancestors were very clever.

C.To tell us the ancient people had a lot of food to eat.

D.To show the ancient people were good at preserving food.

2.Which of the following will the author probably agree with?

A.If you want to make a ham, you should keep it in a brine.

B.If you want to make sauerkraut, you’d better pour on a layer of salt and rub it.

C.To keep our food longer, you should put as much salt on the food as possible.

D.People needn’t give up salty food completely as long as they control the amount.

3.What’s the author’s purpose in writing the text?

A.To explain how the ancient people preserve food.

B.To tell us how salt works in preserving food.

C.To persuade people to give up salty food.

D.To introduce the way of preserving food with salt.