Somebody asked her,（）

1、I have（）her, but I have never met her.

I have（）her, but I have never met her.AheardBheard ofCheard fromDheard a lot

2、She had just finished her homework her

She had just finished her homework her mother asked her to practice playing the piano yesterday.A when B while C after D since

3、She took her handkerchief out （） her p

She took her handkerchief out （） her pocket.AfromBofCi

4、（）的数字调制有ASK。

（）的数字调制有ASK。A恒定包络B不恒定包络C线性包络D语音信号

5、在频带传输过程中，ASK表示（）

在频带传输过程中，ASK表示（）AA.幅度调制BB.频率调制CC.相位调制DD.辅助调制

6、ASK的优缺点是什么？

ASK的优缺点是什么？