It is on September 1ststudents go back to school every year.A. whenB. whoC. thatD. what

问题补充：

It is on September 1ststudents go back to school every year.

A. when

B. who

C. that

D. what

答案：

A. when

B. who

(答案→)C. that

D. what

解析：考查强调句型。强调句型的基本结构：it is/was 被强调成分that/who其它成分。去掉it is/was…that/who…句子仍然成立。本题强调的是时间状语on September 1。句意：正是在9月七日，所有学生都返回学校。故C正确。