根据生产性粉尘的性质可将其分为（）。
A.混合性粉尘
B.无机性粉尘
C.小颗粒粉尘
D.有机性粉尘
参考答案：A, B, D
0℃的冰比0℃的水温度低。[ ]
— Must I go to the gym three times a week?
— No, you _____. Twice a week is OK. [ ]
A. mustn't
B. needn't
C. can't
D. shouldn't
