问题
.The other day I was showing the boys theweekly chemistry experiment when, ________ I knew it, the mixture was bubblingover everywhere.
A:must
B:before
C:though
D:unless
B:before
C:though
D:unless
正确答案是：
同类题型
Where is Jack?— He _________ football on the playground with those AFS students, but I am not sure.
Why did she break away from her family? — Because she wouldn’t _____ that young man.[ ]
The vegetables in the supermarket is very / fre /.
I met the fruit-pickers, several of _______ were still university students.