( )加工可通过透明介质(如玻璃)进行加工。
A．电火花
B．超声波
C．激光
D．切削
参考答案：C
— What were you doing when I phoned you last night?
— I ______ my homework and was starting to surf the Internet.
A．have already finished
B．was finishing
C．was going to finish
D．had just finished
用煤代替焦炭有何利弊？
