载波通信在线路上传输的方式是（）。
A.单边带传输
B.双边带传输
C.载波抑制单边带传输
参考答案：C
18. ---- Are you free after school?
---- Sorry. I’ve planned to treat a friend of mine to dinner _______for his help.
A．in charge
B．in honour
C．in turn
D．in return
核桃嫁接应在（）较少或无的时期进行。
