题目内容：

Space vegetables are grown from seeds (种子) that have been taken to space and brought back to the earth. The seeds are affected by the radiation (辐射) and low gravity in space. When they are brought back to the earth, these seeds produce vegetables that are bigger and healthier than normal vegetables. However, some people worry about eating space vegetables. They think that space vegetables might not be good for us and could make us get sick because of the radiation in space. However, people should not be frightened because space vegetables are very healthy.

Here are some facts that you should know about space vegetables.

Space vegetables are grown from seeds that are carefully chosen. When seeds are brought back from space, they are tested to make sure that they will be safe to eat.

Space vegetables are better for you than normal vegetables. For example, space tomatoes stay fresh for twenty days, which is one week longer than normal tomatoes.

After genetically modified (转基因) food appeared in the market, people worried that they were eating unknown things. For example, if nut genes (坚果基因) are put inside potatoes, people allergic (过敏的) to nuts might get sick from eating these potatoes because they do not know they are also eating nuts. Unlike genetically modified food, space vegetables have not been genetically changed. This means that no new genes are put into the vegetables. Therefore, there are no dangers of eating something unknown.

1.The seeds brought back from space produce ______ vegetables according to the passage.

A. more delicious             B. healthier and bigger 

C. more dangerous             D. cheaper and healthier

2.Genetically modified food is different from space vegetables because it ______.

A. is grown in space             B. has nothing unknown

C. has been genetically changed D. has no new genes

3.According to the passage, normal tomatoes can stay fresh for about ______ days.

A. seven    B. thirteen   C. twenty      D. twenty-seven

4.The writer wants to tell us that ______.

A. space vegetables are grown in space

B. everybody worries about eating space vegetables

C. space vegetables are safe and good for people to eat

D. space vegetables may bring illness to us because of the radiation in space