正弦交流电在一个周期中变化的电角度为（）rAD
A、π／2
B、π
C、π／3
D、2
参考答案：D
— How do you find Qingdao, Mary?
— It's a beautiful seaside city.I have________it for my next holiday.
A. decided on
B. tried on
C. taken on
D. carried on
