矿用防爆电器入井前，应检查其( )及安全性能。
A．产品合格证
B．防爆合格证
C．强度测试合格证
D．煤矿矿用产品安全标志
参考答案：A,B,D
Mary is by no means learned; nor is she good at any practical trade. The only asset she possesses is her beauty.()
A. something valuable
B. temptation
C. something pleasing to the eye
D. womanly virtue
