从每题所给的A、B、C、D四个选项中，选出可以填人空白处的最佳选项，并在答题卡上将该项涂黑。
21．Our teacher asked us to use Internet as resource when we work on our essays•
A．不填；a B．不填；the C．the ; a D．the ; 不填
22．—Are you still employed at the post office?
—Yes，I here since 1982.
A．work B．have been working C．worked D．had been working
