It is said the cost of medical care today is ten times as ____ as it was ten years ago.

A．expensive

B．big

C．high

D．tall

下列哪项不是夜视系统的开启必要条件（）

A.点火开关置于“on”位置

B.微光感应单元认为是黑天

C.前大灯必须开启

D.汽车是运行状态