发电机频率应保持在50Hz运行，其变化范围不超过（）Hz。
参考答案：±0.2
—I have a headache. I can't sleep.
—_______[ ]
A. You are bad.
B. I'm sorry to hear that.
C. Why do you say that?
D. Thank you
热作法施工是指在冬季施工时砂浆用热水拌和的一种施工方法。( )
