ZK-2型通讯控制系统在采煤工作面每（）m设一台扩音电话。
A.8
B.12
C.15
D.18
参考答案：D
The children went home from the grammar school, their lessons（）for the day.
A. finishing
B. finished
C. had finished
D. were finished
刮板的主要技术要求是什么？
