--I hear this kind of CD-ROM is very popular.--Let’s buy one before it .A. is come outB. c

问题补充：

--I hear this kind of CD-ROM is very popular.

--Let’s buy one before it .

A. is come out

B. comes out

C. sells out

D. is sold out

答案：

A. is come out

B. comes out

C. sells out

(答案→)D. is sold out

解析：本题考查动词短语。sell out卖光，不用被动语态。