像be faced with、be based on这样的表达，放在句首为啥省略be？

像be faced with、be based on这样的表达，放在句首为啥省略be？

be faced with、be based on，实际用起来是is faced with、were based on等形式，这是“谓语动词”的形式。

例：He is face with many problems. 他面临着很多问题。

但如果用作非谓语动词，就没有be了，无论是用在句首还是句中。

例：

1. Faced with so many problems, he must do something. 面对如此多的问题，他必须做点什么。

2. The man faced with so many problems must do something. 面对如此多问题的这个人，必须做点什么。

综上，有没有be，取决于用作谓语动词还是非谓语动词。