矿井生产过程中，经常遇到的有害气体有（）。
A、一氧化碳
B、二氧化碳
C、硫化氢
D、二氧化硫
参考答案：A, B, C, D
Jerry was very excited to see the playground ________ she used to play football ________ with lots of snow.
A．where; covered
B．which; covered
C．/; covering
D．where; covering
影响药物用量的药物因素不包括（）。
A.毒性
B.质地
C.功效
D.气味
