improve的名词形式

　　例句：

　　1、An improvement in living standards could be years away.

　　可能多年之后生活水平才能得到提高。

　　2、This may have been an improvement, but "breakthrough" was an overstatement.

　　这算得上是一个改进吧，但说是“突破”就言过其实了。

　　3、Doctors say he has made a slight improvement.

　　医生说他的病情稍有好转。