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问题
单项选择题
钻井时泥包卡钻的原因（）。
A、软底层钻进，适当提高转速控制钻压
B、软底层钻进泵量不足
C、软底层钻进减小钻压
D、粘土层采用粘度小的泥浆
答案
参考答案：
B
选择题
It is the most instructive lecture that I _____ since I came to this school.
A. attended
B. had attended
C. am attending
D. have attended
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名词解释
损耗因数
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