—I didn't ask for the name list. Why______ on my desk?

—I put it there just now in case you needed it.[ ]

A. does it land  

B. has it landed

C. will it land  

D. had it landed

某论坛发帖子系统有如下需求：(1)记录帖子内容：系统对访客的输入内容进行检查，无非法内容，则将内容存入发帖内容文件中，否则提示内容非法。(2)显示帖子内容：从发帖内容文件中读出帖子内容，按一定格式显示在屏幕上。请根据要求：(1)画出该子系统的数据流图；(2)将其转换为软件结构图。