面粉厂运进200吨面粉记作+200,那么运出50吨面粉记作______.
“运进”与“运出”相对,所以,若运进200吨面粉记作+200,那么运出50吨面粉应记作-50.
The old engineer's eyes still shone bright in the wrinkled brown face and his step as he came across
the room was________,though slow. [ ]
A. shaky
B. heavy
C. casual
D. steady
对于溶解性气体或挥发性有机物所产生的臭和味,可采用______去除。
A.微滤机或气浮法 B.曝气法C.除盐措施 D.活性炭吸释或氧化法