21.It was not until he arrived in class

21.It was not until he arrived in class

这个有问题,我觉得是It was not until he arrived in class did he realized that he had forgotten his book.======以下答案可供参考======供参考答案1:题抄错了吧供参考答案2:that he供参考答案3:同学，选项呢。。。后面应该用倒装供参考答案4:that强调句啊！！供参考答案5:是强调句型，不过你的句子写错了。应该是：It was not until he arrived in class that he realized he had forgotten his book.供参考答案6:这句话可以说成not until he arrived in class did he realized ....如果要是强调句 即去掉it is 和and 句子意思仍然完整故为 it was not until he arrived in clss that he realized.....

这个解释是对的