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【多选题】
矿用电机车直流电动机用直流斩波器改变加在电动机两端的平均电压而实现调速，直流斩波器调压方式有()A.
调宽式
B.
调频式
C.
调频调宽式
D.
定频式
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【单选题】-- Did you visit the zoo? --- No, we_______have visited it, but we spent too much time shopping.
A.
shouldn’t
B.
can’t
C.
could
D.
must
【单选题】— We want someone to design the art museum for us. — _____ the young fellow have a try?
A.
May
B.
Shall
C.
Will
D.
Need
【简答题】1) As to the steamer sailingfrom SH to Los Angeles, we have bimonthly direct services. 2) We would like to knowwhether you would allow us to extend the time of shipment for twenty days andif you would...
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