Just as sound travels through the air in waves, electricity travels through the air in radio waves.
A. what is called
B. which is called
C. what it is called
D. which it is called
网友回答
(答案→)A. what is called
B. which is called
C. what it is called
D. which it is called
解析：本题考查名词性从句。介词in后面的宾语从句中缺少主语，故用what做主语，故选A。