火力发电厂排出的烟气会造成对大气的污染,现代大型电厂的主要污染物是( )。
A. 二氧化碳和二氧化硫
B. 粉尘和二氧化碳
C. 二氧化硫和氮氧化合物
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检修周期是指相邻两次( )之间的间隔时间。
A. 小修
B. 临修
C. 大修
Which statement is NOT true about this conversation
A. It took place on Sunday.
B. It took place between two classmates.
C. It took place in the evening.
D. It is about asking for a favor.
How many people died in riots on Tuesday
A. 13.
B. Unknown.
C. 36.
D. 300.
钢的热处理是先把钢加热到高温，使组织转变为（ ），再以一定速度冷却下来，从而获得需要的组织与性能。
A. 奥氏体
B. 渗碳体
C. 铁素体
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