按污染源释放的有害物质种类分类,水体废气物的来源可以分为()。
A.物理性污染源
B.化学性污染源
C.生物性污染源
D.人文性污染源
参考答案:A, B, C
Not believing their eyes, the visitors on the spot _______ the flying plane, doing some most difficult and dangerous tricks in the sky.
A.glared at
B.stared at
C.glanced at
D.caught sight of
城市燃气管网投产置换用的气体一般为()。