储罐储存了原油后因呼吸阀损坏而发生事故，则该事故的危险源是（）。
A.储罐
B.呼吸阀
C.原油
D.截止阀
参考答案：B
Waste paper shouldn't everywhere .It's our duty to keep our city clean.[ ]
A. be thrown
B. throw
C. is thrown
D. are thrown
如何评价马尔萨斯的《人口原理》。
