题目内容：
What caused the American scientists to work on special trees?
参考答案：
答案解析：
单选题：What caused the American scientists to work on special trees
- 题目分类：英语
- 题目类型：单选题
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Lessons_____________ easily are soon forgotten.（ ）
Lessons_____________ easily are soon forgotten.（ ）
下列情形中，诉讼时效为1年的是（ ）。
下列情形中，诉讼时效为1年的是（ ）。
Several leading teams were sent in order to___________.
Several leading teams were sent in order to___________.
We know from the last paragraph that the author___________.
We know from the last paragraph that the author___________.
请根据下面提示，写一篇短文。词数不少于50。
请根据下面提示，写一篇短文。词数不少于50。