题干
.
It was _____ his mother came in _____ to prepare his lessons.
It was _____ his mother came in _____ to prepare his lessons.
A：not until; did the boy begi
B：until; that the boy didn’t begi
C：until; did the boy not begi
D：not until; that the boy bega
答案(点此获取答案解析）
D
实验二： 
实验三： 