三相异步电动机采用三相六拍通电方式，步距角为1.5°，改为三相单三拍时步距角为（）。
A、1.5°
B、3°
C、0.75°
参考答案：B
This kind of glasses made by experienced craftsmen ______ comfortably.[ ]
A. is worn
B. wears
C. wearing
D. are worn
设已知等差数列{an}满足a1+a2+…+a101=0，则有（ ）．
A．a1+a101＞0
B．a2+a102＜0
C．a3+a99=0
D．a51=51
