I don't know when ____ famous. [ ]
A. does he become
B. he becomes
C. did he become
答案:B
脊髓灰质炎的隐性感染率为()
A.50%
B.90%
C.60%
D.80%
E.70%
软件生命周期分为软件定义期、软件开发期和软件维护期,详细设计属于______中的一个阶段。