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【简答题】
已知某 调幅波表达式为: u AM ( t)= 20(1 +0.2cos100πt ) cos10 7 πt ( V) , 求 : (1) 调幅度 m a ; (2) 通频带 ( 带宽 ) ;( 3 )调制信号频率; ( 4 )调幅类型。
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【单选题】Allen wanted to know ____ after it got out of the UFO.
A.
what is the alien doing
B.
what the alien would do
C.
where would the alien go
D.
where the alien is going
【单选题】The author pointed out all the following facts EXCEPT that ______.
A.
to eliminate alien species for the sake of the indigenous ones is also ecological imperialism
B.
humans efforts to correct ecological disorders is actually based on human preference
C.
people's attitudes towards alien species involve moral considerations
D.
human have to design nature to protect biodiversity
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