以下行为中不属于邮件服务器维护的范围是（）
A.升级邮件服务
B.过滤垃圾邮件
C.安装配置邮件服务
D.删除过期邮件
参考答案：B
Where to go for a holiday ______ yet. [ ]
A. has not been decided
B. have not been decided
C. are not decided
D. isn't being decided
缩窄性心包炎（）。
A.肺性发绀
B.心性混合性发绀
C.淤血性发绀
D.缺血性发绀
E.混合性发绀
