He has worked in the city _______ three years ago while his wife has been here______only one month.

A．since , for

B．since, since

C．for, since

D．for, since

检验检测机构的文件可承载在各种载体上，可是硬拷贝或是电子传媒，也可是数字的、模拟的、摄影的或书面的形式。