问题
选择题
This kind of CD-ROM is very popular. Why not buy one before it________ ?
A.comes out
B.is come out
C.sells out
D.is sold out
答案
答案:D
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