开采放射性矿物的矿井，必须采取严格管理井下污水等措施，减少（）析出量
A.氮气
B.氧气
C.氡气
参考答案：C
—Peter was sick badly and the doctor advised him to for two weeks.
—It’s terrible. I think we should go to visit him.
A．hit
B．cheer
C．rest
D．repair
美国需要进口而巴西可以向其大量提供的农产品是[ ]
A．乳肉
B．玉米
C．小麦
D．咖啡
