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【判断题】
一定量的水,从海洋蒸发变为云,山上变为雨、雪,并凝结成冰。冰、雪熔化变成水流入江河,最后流入大海,一定量的回到始态。问历经整个循环,水的热力学能和焓的变化均为零。A.
正确
B.
错误
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【简答题】中国网球协会成立1956年10月23日，（）任。
【单选题】By the time I got to the cinema, the movie _______ for ten minutes. [ ]
A.
had begun
B.
had been on
C.
has started
D.
has been on
【简答题】某台三相鼠笼式异步电动机,绕组为Δ接法, λ=2.5,KT=1.3,供电变压器容量足够大,该电动机_______用Y-Δ启动方式拖动额定负载启动。
【单选题】By the time I got to the train station, the train _______ for ten minutes. I had to wait for the next one. [ ]
A.
has left
B.
has been away
C.
had left
D.
had been away