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【单选题】
Positive displacement, helical gear(斜齿轮) pumps are well suited for pumping oil because ______.
A.
stuffing boxes eliminate the leakage problems usually associated with other gear pumps
B.
it is not necessary to closely maintain design clearances with this pump
C.
they are essentially self-priming and produce a high suction lift
D.
these pumps are designed with extreme tooth angles
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参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】Passage 3 Questions 11 to 15 are based on the following passage: Scientists in India have invented a new way to produce electricity. Their invention does not get its power from oil, coal or other fuel...
A.
Because bullocks have long been used by Indian people
B.
Because bullocks walk slowly and are easy to control.
C.
Because there are few non-working bullocks in India
D.
Because there is not enough oil in India.