注意：此页面搜索的是所有试题
题目内容
（国家开放大学英语语法）
Only when class began _______that he had left his book at home.
A. will he realize
B. he did realize
C. did he realize
D. should he realize
A. will he realize
B. he did realize
C. did he realize
D. should he realize
参考答案