电热水袋中的水加热后袋子膨胀，是因为袋内的水（   ）

根据短文内容判断正误，正确的写正确，错误的写错误。

                                                                                                (C)

    The best-known (最熟知的) vegetable in the world is the potato. It grows in many places and does not need rich soil(土壤) like many other crops. But until four hundred years ago, the Europeans(欧洲人) began to know the potato. But today it's one of the main foods in Europe(欧洲). About half of the world's potatoes are grown in Europe.

    In France the potato was not grown for a long time .Here is story about Louis. In 1778 he saw some potato flowers for the first time .He liked them so much that he picked one and put it in his buttonhole. He was interested in the flowers not the potatoes themselves.

调查时首先要明确____和____，制定合理的____．调查的范围很大时，就要进行____，调查过程中要如实____．对调查的结果要进行____和____，有时要用数学方法进行统计．