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在通信系统的接收端，高放电路的作用是（ ）
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在通信系统的接收端，混频电路的作用是（ ）
在通信系统的接收端，本振电路产生的振荡信号的频率要比送到混频器的某个频道的调制信号的载频差出一个固定的频率。（ ）
spend cost golden usual explore require experiencetemporary lifelong businessmen various develop scholarslay foundationYou will 1) ________ at least four years in college. College days will be the 2) ________ time in your life. There are many opportunities for you to 3) ________ the unknown and you can 4) ________ a lot. You can make 5) ________ friends; you can enjoy 6) ________ kinds of activities; you can 7) ________ your personal interests; and you will meet some outstanding 8) ________. Keep a good balance and 9) ________ a solid foundation. There are many doors to your dreams. You decide how many you can open.
Fill in the blanks with the proper words.（填入适当的词来完成句子。）1. It is quite natural that my coming late again ________ them very angry.2. He acted as if he ________ everything in the world.3. Read it aloud so that I ________ you clearly.4. They got up early in order that they ________ they first train.5. That is a good book. You ________ it yesterday.6. I insisted that he ________ at once.7. Do you think of Wang Fang's suggestion that he ________ Mr. Li to the party?8. He asks that he ________ an opportunity to explain why he's refused to go there.9. My sister advised me that I ________ accept the invitation.10. His mother wishes that he ________ be tall when he grows up.
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