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【单选题】
( ) 控制比较简单,多用于通用变频器在风机、泵类机械的节能运转及生产流水线的工作台传动等。A.
U / f
B.
转差频率
C.
矢量控制
D.
直接转矩
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【单选题】Since the auto is the main source of travel in America and distances between major cities are far, a common way of getting around the country is by hitchhiking. Although it is not illegal, law enforce...
A.
It is a good way for children.
B.
It is illegal in America.
C.
It may involve dangers.
D.
It must be totally stopped,
【单选题】Tests Show Women Suited for Space Travel Between 1977 and 1981, three groups of American women, numbering 27 in all, between the age of 35 and 65, were given month-long tests for space travel purposes...
A.
At the end of ten years, they had to spend a further twenty days absolutely confined to bed.
B.
They were volunteers and were paid barely above the minimum wage.
C.
These tests were conducted to determine how they would respond to conditions resembling those abroad the space shuttle.
D.
They need less food and less oxygen and they stand up to radiation better.
E.
Some of them were over 65.
F.
When they were finally allowed up, the more physical active women were specially subject to pains due to a slight calcium (钙)loss.
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