—When did he leave the classroom?—He leftyou turned back to write on the blackboard.A. the

问题补充：

—When did he leave the classroom?

—He leftyou turned back to write on the blackboard.

A. the minute

B. the time

C. until

D. before

答案：

A. the minute

B. the time

C. until

D. before

解析：the minute=as soon as，一…..就…..，你一转身，他就离开了。故选A。