his是物主代词,不能作主语；

作主语的可以是he或是she；

当主语是单数第三人称时,后面的动词要用单数第三人称形式,简称单三形式,规则的动词在其后加s即可。

You could see from his face that he was lying.

从他的.表情上你可以看出他在说假话。

The operation could prolong his life by two or three years.