because什么词

　　They are here because of us.

　　他们是因为我们来这里的。

　　We couldn't understand them because they were talking in Chinese.

　　我们听不懂他们在讲些什么，因为他们说的是汉语。

　　His school work is suffering because of family problems.

　　由于家庭问题，他的学业日渐退步。