常常看到书上说（老师上课也常常说）：不定式的进行式，不定式的完成式，不定式的被动式，等等，请老师给讲解一下，同时举几个例子。不要太多，也不要太难，谢谢老师！
▲不定式的进行式：to be doing（即在 to be 后接目前分词）
He seemed to be sleeping. 他好像在睡觉。
He appears to be living in the area. 他好像就住在这一带。
He believed her to be telling the truth. 他相信她讲的是真话。
▲不定式的完成式：to have done（即在 to have 后接过去分词）
She appears to have caught cold. 她仿佛是感冒了。
He seems to have travelled a lot. 他好像去过不少地方。
I believed it to have been a mistake. 我相信这是一个错误。
We consider him to have left. 大家觉得他已离开。
▲不定式的被动式：to be done（即在 to be 后接过去分词）
Your hair needs to be cut. 你需要理发了。
He begged to be allowed to go home. 他恳求让他回家。
I was disappointed not to be chosen. 我未被选中，感到非常失望。
It is an honor to be invited to contribute to your magazine.承蒙贵刊邀稿，甚感荣幸。
