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【单选题】
定常流动是（ ）。A.
流动随时间按一定规律变化
B.
流场中任意空间点上的运动要素不随时间变化
C.
各断面的速度分布相同
D.
速度为常数
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举一反三
【简答题】企业生命周期中最危险的阶段是()。 A、婴儿期 B、青春期 C、盛年期 D、官僚期
【单选题】Mrs. Black doesn't believe her son is able to design a digital camera, ______? [ ]
A.
is he
B.
isn't he
C.
doesn't she
D.
does she
【单选题】Mrs. Black doesn’t believe that her son is able to design a digital camera, ______?
A.
is he
B.
isn’t he
C.
doesn’t she
D.
does she
【单选题】I don't believe Jim is able to design a digital camera, ______? [ ]
A.
is he
B.
isn't he
C.
doesn't he
D.
does he
【单选题】Black doesn’t believe his son is able to design a digital camera,_____?
A.
is he
B.
isn’t he
C.
doesn’t he
D.
does he
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