【题目】It was only after she had read the papers _______ Mary realized the homework before her was extremely difficult to complete.
A. when B. that C. which D. what
在线课程【答案】B
【解析】
试题分析：本句为强调句。强调句的结构：It is/was+被强调部分+that....；本句中被强调的部分是时间状语从句only after she had read the papers，故空缺处要填that,故选B。