考试高频点：虚拟语气中if（的省略）

虚拟语气的重要用法之一就是在事实相反或者很难实现的条件下会发生事情的描述。if条件句是很重要的一环。

如：

If I were a bird， I would be able to fly in the air. 如果我是鸟，我就会飞在空中了。 (从句过去式，用were代替was，主句 would+动词原形）。

If I were you，I would go at once. 如果我是你，我就会马上走。

但考试中经常出现的一个考点是省略IF 的情况， 当从句的谓语动词含有were，should，had时，if可以省略，这时从句要用倒装语序，即把were，should，had等词置于句首，这种多用于书面语。 如：

Were he free， we would have sent him to the construction site. 如果他有空的话，我们就派他去施工现场了。 （=If he were free， we would have sent him to the construction site. )

Had he known the truth, we could have communicated with him on this issue freely. 如果他知道事实的话，我们就可以就此事自由的与他沟通了。 （ =If he had known the truth）