轴流式风机的工作范围较宽阔。
参考答案：对
You should understand the math problem now, you have had it ______ three times. [ ]
A. explaining
B. to explain
C. explained
D. explain
据焊接管坡口要求，管壁厚度超过（）时就需坡口，其坡口要求为3mm，
A、4mm
B、6mm
C、8mm
D、10mm
