按国标GB16297-1996规定硝酸生产尾气氮氧化物气筒(60m高)最高允许排放速率(kg/h)三级为()。
A.21
B.23
C.25
D.27
参考答案:C
--- It’s difficult for the village children to cross the river for school.
--- I think a bridge ________ over the river.
A.should be built
B.is being built
C.has been built
D.was built
开启对象捕捉功能的快捷键为()
A.F1
B.F2
C.F3
D.F4