【推荐1】喇叭裤是二十世纪六十年代末期时装流行不可缺的。
Bell bottoms were a fashion must ________ .

【推荐1】我们之所以选择这部电影，是因为它代表了我们学校的发展，这不仅有趣，而且有意义。
The reason _____we choose this movie is that it represents the development of our school, which is not only interesting but also meaningful.

【推荐2】看到苹果落下的人不计其数，但牛顿是第一个问为什么的。
Millions of people saw the apple fall, but Newton was _________.

【推荐3】Lisa wrote the letter to say goodbye to her junior teacher. (对划线部分提问)
________ ________Lisa write the letter?

【推荐1】那就是为什么每次太空行走都要精心计划。
_________________ every spacewalk is carefully planned.

【推荐2】这就是为什么我们应该关心野生动物的生存条件。
This is ________________ the living conditions of wild animals.