异步电动机定子的三相绕组可有（）种接法。
A、1
B、2
C、3
D、4
参考答案：B
China's first spaceman, Yang Liwei, with Shenzhou V ______successfully to earth on Thursday morning after more than 21 hours’ travel along the earth's orbit. [ ]
A. returned back
B. arrived
C. reached
D. returned
如何对建筑物冻害进行维护？
