This kind of CD-ROM is very popular. Why not buy one before it ?
A. es out
B. is e out
C. sells out
D. is sold out
网友回答
A. es out
B. is e out
C. sells out
(答案→)D. is sold out
解析：短语辨析。Come out 是出来，出现的意思。sell out 是卖完的意思，句意：这种光驱非常受欢迎。为什么不在它买完之前买一个？结合语境可知it是卖完的对象，故用被动语态，故选D