当斜槽或风管堵塞时，用手锤敲击检查时声音是（）
A、清脆
B、沉闷
C、无声音
参考答案：B
It's raining outside. So please my umbrella, but don't forget to ______ it back tomorrow.
[ ]
A. take; take
B. bring; take
C. take; bring
D. bring; bring
危险废物填埋场场界应位于居民区( )以外，并保证在当地气象条件下对附近居民区大气环境不产生影响。
A．500m
B．600m
C．700m
D．800m
