这是个强调句,被强调部分在句子中作主语,所以用she.
She cleaned the classroom yesterday.那如何判别它是一个强调句呢It is +强调部分 +that/who+其他部分。强调部分是人用who, 否则用that那被强调部分是短语还是句子还是什么？出句子中的谓语部分外都可以。Itwas the classroom that she cleaned yesterday.It was yesterday that she cleaned the classroom.