单选题Positive displacement, helical gear pumps are well suited for pumping oil because （）Astuffing boxes eliminate the leakage problems usually associated with other gear pumpsBit is not necessary to closely maintain design clearances with this pumpCthey are essentially self-priming and produce a high suction liftDthese pumps are designed with extreme tooth angled
单选题
Positive displacement, helical gear 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 angled
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