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【简答题】
正弦波脉宽调制（SPWM）变换器的作用是：把恒定的直流电源电压调制成频率一定、（）可变的脉冲电压系列，从而可以改变平均输出电压的大小，以调节电机转速。
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举一反三
【单选题】— It's Father's Day today, _____? —Yes, let's buy a gift for Dad.
A.
isn't he
B.
doesn't he
C.
isn't it
D.
doesn't it
【单选题】Two men ___ into my flat. One of them threatened me with a knife while the other tied me up.
A.
found their way
B.
pushed their way
C.
wound their way
D.
made their way
【单选题】Although ______ for many years, the two old sisters recognized each other at once.
A.
having been separated
B.
being separated
C.
having separated
D.
had been separated
【单选题】Speaker A: It's a beautiful day today! How about a little trip out into the country? Speaker B: ______
A.
That sounds great. What should I do for the preparation?
B.
I don't know. I really haven't thought about what should do.
C.
Well, would you like me to pack picnic or to buy something?
D.
It's all right. Thank you.
【单选题】--- The two old friends were ______ busy _____with each other ______ the time. --- Yes. They haven’t met for long.
A.
too, to talk, to forget
B.
too, talking; to forget
C.
so, to talk, that they forgot
D.
so, talking, that they forgot
【单选题】The apples are divided _____ two _____. One is for my sister, the other is for me. [ ]
A.
in; half
B.
into; halves
C.
in; halves
D.
into; halfs
【单选题】Potash (the old name for potassium carbonate) is one of the two alkalis (the other being soda, sodium carbonate) that were used from remote antiquity in the making of glass, and from the early Middle ...
A.
How it was made.
B.
Its value as a product for export.
C.
How it differs from other alkalis.
D.
Its importance in colonial North America.
【简答题】比丘国王要取( )个男孩心肝做药引。孙悟空假扮唐僧,当场剖腹,摘出红心、白心、黄心、悭贪心、利名心、( )心、( )心、好胜心、望高心、侮慢心、杀害心、( )心、( )心、( )心、( )心、无名隐暗之心,种种不善之心,更无一个黑心。
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