调制解调器是按被调制参数进行分类,属于线性调制的应()。
A.不在下述选项中
B.是调频
C.是调相
D.是调幅
参考答案:D
John fell asleep _________ he was listening to the music.
A.after
B.before
C.while
D.as soon as
高压厂用母线一般采用单母线,而低压母线则采用单母线分段。()