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【简答题】
This “noctilucent cloud” occasionally appears when the earth is first cloaked in the evening darkness.
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举一反三
【单选题】— Space travel must be very very expensive. — . The cost of a seat on the Virgin craft is $ 250,000.
A.
That’s not true.
B.
Of course.
C.
Why do you think so?
【单选题】—The poor people lived near the highway. —_____ very noisy.
A.
It must have been
B.
They must be
C.
That might be
D.
There must be
【单选题】You must be very careful when handling these acids______they are very concentrated.
A.
as
B.
when
C.
if
D.
while
【简答题】由CMOS门电路组成的施密特触发器如图7．1．3(a)所示，已知R1=5 kΩ，R2=10 kΩ，VDD=5 V，VOH≈5 V，VOL1≈0 V，VTH1=2．5 V。 (1)计算正向、负向阈值电压及回差电压。 (2)当阈值电压变为 时，若使回差电压不变，对电阻有何要求?此时正向、负向阈值电压为何值?
【简答题】机器可以用来代替人的劳动,完成有用的
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