—Now that you like the house with a garden, why not buy it
—Well, I can't afford （） house at present.

A. that expensive a

B. a such expensive

C. that an expensive

D. a so expensive

UNIX 系统中，输入/输出设备被看成是下列四种文件的______。

A．普通文件

B．目录文件

C．索引文件

D．特殊文件