通常竖炉四大循环气体分别为（）、（）、冷却风、蒸汽。
参考答案：煤气；助燃空气
To make believe that there was still someone in the house, the housewife went downstairs, ______ the lights ______ in the living room.
A．left; burnt
B．leaving; burning
C．leaving; burnt
D．left; being burnt
薄层层析所用展开剂主要是（）的有机溶剂，一般使用2~3种组分的多元溶剂系统。
A.高熔点
B.低熔点
C.高沸点
D.低沸点
