在英语中，我们常用It is／was… who/that结构来突出强调句子的某一成分(一般是句子中主语，宾语或状语)。在这个句型中，it没有词汇意义，只是引出被强调的成分。如果被强调的成分是表示人的词，用who或that来连接都可以。如果是其它成分，则一律用that来连接。
E.g. It is my mother who／that cooks every day.
E.g. It was yesterday that Tom passed in the maths exam．
e.g. It is I who am right．
e.g. It is he who is wrong．
e.g. It is the students who are lovely．
2．即使被强调成分是句子中的时间状语，地点状语，原因状语等，也不能用when，where, because，要用 that。
E.g. It was after the war was over that Einstein was able to come back to his research work again .
E.g. It was in front of the bank that the old lady was robbed．
E.g. It was because of the heavy rain that he came late．
It was from him，his chemistry teacher，that Paul learned to watch carefully in class．
It was he that helped me yesterday.
It was me that he helped yesterday.
lt was the things and people that they remembered that they were talking about．
三、区分定语从句和强调句型某些定语从句和强调句型形式差不多，容易混淆。如果去掉it is／ was ...that句子仍然通顺成立，则为强调句型，不成立不通顺，则为定语从句。
E.g. It was three years ago that he went to American for a further study·去掉It was that句子为Three years ago he went to America for a further study．句子通顺，意思完整，那么，这就是一个强调句型。