空压机微热再生吸附干燥机及过滤装置,是作为空压机的配套设备,有效地除去压缩空气中含有的()等杂质,使压缩空气达到要求的()。
参考答案:水份、油、粉尘;质量等级
计算:(﹣x4)3= ,﹣2a(3a2b﹣ab)= .
The air in Beijing is getting much ______ now than a few years ago.[ ]
A. clean
B. cleaner
C. cleanest
D. the clcanest