一、as if用得普遍些，却可引导
方式状语从句和表语从句，其从句谓语常用
虚拟语气。
(1)引导方式状语从句
e.g.He closed his eyes as though he were too tired.
他闭着眼睛，好像太累了。
She acted as though nothing had happened.
她装得好像什么事也没发生过似的。
当从句主语和主句主语一致，从句谓语中又含有动词to be时，可以把主语和to be
一起省去。
e.g.He looked about as though (he was)in search of something.
他四下张望，好像寻找什么。
He paused as if(he was)expecting Tom to speak.
他停了下来好像期望Tom说些什么。
He listened as though he was turning to stone.
这孩子一动不动地听着，仿佛变成了石头似的。
(2)引导表语从句
e.g.It looks as if it"s going to rain.
看样子天要下雨了。
It seems as if I"m the first one here.
看起来我是第一个到这里的。
as though和as if从句用虚拟语气，还是用陈述语气。完全根据具体情况而定。如果
从句表示的意思与事实完全相反，或者纯粹是一种假设，通常用虚拟语气。
e.g.When a pencil is partly in a glass of water.it looks as if it were
broken.
当铅笔一部分放进水里，看起来好像折断了似的。(虚拟)
You look as if you are friends.
你们看起来像朋友似的。