对于沥青混合料试件，若能用水中重法测定其表观密度，则也可用表干法测定其毛体积密度，而且两种方法的测试结果会比较接近。( )
参考答案：对
下列物质属于纯净物的是（ ）
A．酱油
B．空气
C．蒸馏水
D．铜锌合金
Walmart, which is one of the largest American supermarket chains, ________ some of its stores open
24 hours on Mondays through Saturdays. [ ]
A. keeps
B. keep
C. have kept
D. had kept
