连系动词 be 后根据情况可自由地接不定式作表语：

My dream is to be a scientist. 我的梦想是当一名科学家。

All you have to do is to listen. 你只需要听。

seem, appear, prove, turn out, grow 等连系动词后也可接不定式(尤其是 to be)短语作表语：

The man seemed to be ill. 这个人好像病了。

The plan proved to be useful. 这个计划证明是有用的。

He appears to know this. 他好像知道这一点。

The weather turned out to be fine. 天气结果很好。

He has grown to like studying English. 他渐渐喜欢学英语了。

若所接不定式为to be，通常可以省略。

sound, smell, feel, taste, become 等连系动词后通常不能接不定式：

误：These oranges taste to be good. (应去掉 to be)

误：The roses smell to be nice. (应去掉 to be)

连系动词look后有时也可接to be，但以省略to be 为普通。