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【单选题】
有关混频，以下说法错误的是（　）
A.
混频只适用于振幅调制信号，不能应用于调频、调相信号
B.
混频不改变已调波携带的调制信号的信息
C.
无线电接收机通过下混频降低已调波的频率
D.
普通调幅信号经过混频，包络线不变，波形的振荡频率变化
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【单选题】Black asked me, “ Why haven’t you left here yet?” Black asked me why ____ yet.
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【简答题】完形填空 When I was in primary school, I got into a major argument with a boy in my class. I can't 1 what it was about, but I have never forgotten the 2 I learned that day. I was 3 that I was right and he...
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相关题目：
【单选题】读者进入阅览室优疑难问题需要解决时,应该怎样?
A.
问同学
B.
自己解决
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【单选题】Black asked me, “ Why haven’t you left here yet?” Black asked me why ____ yet.
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【单选题】Those in the language (English) group are different from those studying maths in that______.
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B.
those in language group find it too difficult to continue
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only the language group attend evening classes
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the maths group improve their ability steadily
查看完整题目与答案
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A.
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查看完整题目与答案
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【简答题】完形填空 When I was in primary school, I got into a major argument with a boy in my class. I can't 1 what it was about, but I have never forgotten the 2 I learned that day. I was 3 that I was right and he...
查看完整题目与答案