it is ______that/who当去掉“it is that/who”仍可成为一句话，那么就是强调句例如：It was in the park that they had a picnic yesterday.可变为：They had a picnic in the park yesterday.我觉得这种方法是最容易记住的，比那些语法里的术语要好记，当然你也可以看看语法书。
