HPb59-1表示平均含铜量为59%、含铅量小于1%的铅黄铜。()
参考答案:错
Every few years, the coal workers ___________ their lungs X-rayed to ensure their health.
A.are having
B.have
C.have had
D.had had
煤和悬浮液在定压箱混合后靠自重进入旋流器,定压箱的高度(与旋流器直径)的关系约为()
A、H≥8D
B、H≥9D
C、H≤8D
D、H≤9D