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问题
判断题
及时回柱放顶可减小支承压力。
答案
参考答案：
对
选择题
220, 309 should be read ______.
A. two thousand and twenty thousands, three hundred and nine
B. two hundred and twenty thousand and three hundred and nine
C. two hundred and twenty thousands and three hundred and nine
D. two hundred and twenty thousand, three hundred and nine
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单项选择题 A1型题
饮用水消毒的主要目的是（）
A.保持水中的余氯
B.改善水物理性状
C.消灭大肠杆菌
D.杀灭病原菌预防介水传染
E.消灭虫卵，预防血吸虫病
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