★That is because ...表示原因或理由；That is why ...则表示由于某种原因所造成的结果。如：

Bruce did not watch the game last night. That was because he had to help his little sister with her homework.

Bob had seen the film before. That was why he did not see it yesterday.

三、宾语从句

★用作宾语的从句叫做宾语从句。如：

As a friend of you, I want to tell you what I hear.

Amy was curious to know where we had been.

★that在引导宾语从句时无实际意义，也不充当任何成分，且通常可以省略。但如果含有两个或两个以上的并列宾语从句时，通常只有第一个从句的that可以省略，其余从句的that一般不省略。如：

The guide told him (that) they were on a trip across Canada and that they had only one day in Montreal.

★宾语从句既可以作动词的宾语也可以作介词的宾语。如：

I felt that she had a strong will.

Emily was shocked by what she had seen.

★if引导的宾语从句只能作动词的宾语，且if后不能直接跟or not（需将or not放在句尾）。如：

He stopped to ask me if I was all right.

He didn't say if he would be staying here or not.