第一句不是;其他都是
强调句:
It's +被强调部分+that/who+其他部分
例:
He didn't come to school yesterday because he was ill.
主语强调:It's he who didn't come to school yesterday because he was ill.
时间状语强调:It's yesterday that he didn't come to school because he was ill.
原因状语强调:It was because he was ill that he didn't come to school yesterday.