—Is Bob doing homework?

—No, he ______. He is ______ a letter. [ ]

A. doesn't,write

B. isn't, writes

C. isn't, writing

D. isn't, writeing

数据库系统的日志文件用于记录下述( )内容。

A．数据更新操作

B．数据查询操作

C．程序执行结果

D．程序运行过程