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【单选题】
变频器调速过程中,为了保持磁通恒定,必须保持( )A.
输出电压U不变
B.
频率f不变
C.
U/F不变
D.
U.F不变
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举一反三
【单选题】I think I was at school,____ I was staying with a friend during the vacation when I heard the news.
A.
or else
B.
or so
C.
and then
D.
even so
【单选题】----____? ---- It's very hot.
A.
What day is it today
B.
It's a fine day, isn't it
C.
Do you like the day
D.
How is the weather in Nanjing
【单选题】— _________ — It’s very hot.
A.
What bad weather ！
B.
It’s a fine day, isn’t it ？
C.
Do you like the day ？
D.
How is the weather in Nanjing ？
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