碳素钢与合金钢是按化学成份分类的，而优质钢与普碳钢是按质量分类的。
参考答案：对
— ______. I don't hear you clearly, It's too noisy here.
— I was saying that the party was great. [ ]
A. Repeat.
B. Once again?
C. Sorry?
D. So what?
在计算8、9度罕见地震时，建设场地的特征周期应（）。
A.增加0.1s
B.减少0.1s
C.增加0.05s
D.减少0.05s
