Danby left word with my secretary ________ he would call again in the afternoon.

A．who

B．that

C．as

D．which

使用ifstream流类定义流对象并打开磁盘文件时，文件的隐含打开方式为( )。

A) ios::in
B) ios::out
C) ios::inlios::out
D) 没有默认