根据句意和汉语提示，填写恰当的短语完成下列句子。

1. I hope you can come back___________ (尽快地).

2. All the teachers ____________(乐意帮助) students to solve their problems.

3. We should ___________(坚持) our dreams and try to achieve them.

4. ____________(数以千计的) students were surveyed about their favorite foods.

5. My sister _____________(梦想) becoming a singer. She likes singing very much.

分子束外延生长有什么特点？