单相半波可控整流电路电阻性负载，控制角α=900时，输出电压Ud是()。
A. 0.45U2
B. 0.225U20.5
C. U2
D. U2
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Which of the following is true about the recent annual study ？
A. It is sponsored by 163 countries .
B. It excludes GDP as an indicator.
C. Its criteria are questionable .
D. Its results are enlightening .
A.in the face ofB.in the form ofC.in the way ofD.in the name of
A. in the face of
B. in the form of
C. in the way of
D. in the name of
我国煤矿井下人身安全电流极限值为()
A. 37mA
B. 36mA
C. 35mA
D. 30mA
一个3X(3)A三相电度表欲测10KW三相电动机的电能，应将电度表的电流线圈（）接入负载
A. 串联一个电阻
B. 并联一电阻
C. 经电压互感器
D. 经电流互感器
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