下列各组物品中，通常情况下属于绝缘体的是

A．陶瓷盘、玻璃杯

B．人体、塑料尺

C．橡胶垫、浓盐水

D．铁钉、食用油

It was announced that only when the fire was under control          to return to their homes.

A．the residents would be permitted

B．had the residents been permitted

C．would the residents be permitted

D．the residents had been permitted