当开关断开时，电源处于开路状态。电源的端电压UO称为（）。
A. 开路电压
B. 空载电压
C. 负载电压
D. 内阻电压
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请问城市居民委员会选举一共有几种方式？
A. 一
B. 二
C. 三
D. 四
---_____ is George _____? ---George's working hard.
A. How, work
B. How, working
C. What, working
D. What, work
---______ must Amy _____? ---Amy must sweep the floor.
A. How ， doing
B. How, do
C. What, do
D. What, doing
---______ ______ is George going to paint the bookcase? ---George's going to paint the bookcase pink.
A. What color
B. What colors
C. How colors
D. How color
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