1、在作主语时，如to read english aloud is very important，或者it's very important to read English aloud.大声朗读英语是很重要的
3、在作定语时，如i must find a man to talk, 我必须找一个人聊天，或 i have nothing to do，我没有可以做的事情
5、作补语时，如he asked me to do homework他叫我写作业，He was asked to finish the work他被叫去完成这个工作
