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【单选题】
单层细石英砂滤池，石英砂d10=0.55mm，厚800mm，洗砂排水槽槽底高出砂面360mm，准备移出350mm厚的砂滤料，然后装入d10=0.85的无烟煤滤料补充，已知无烟煤在反冲前后空隙率分别为m0=0.407，m=0.62，则放入的无烟煤厚度是（）。
A.
281mm
B.
325mm
C.
350mm
D.
400mm
参考答案：
参考解析：
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举一反三
【单选题】When stars like our Sun die, they bloat to become red giants and then eject gigantic clouds of gas and dust into space. Increasingly, however, scientists found themselves at a profound loss to explain...
A.
explain-the possible way of death of our Sun.
B.
show the two types of red giants.
C.
discuss on the way of red giants to become white dwarfs.
D.
explore the origin of life.