正确答案: C

they are essentially self-priming and produce a high suction lift

题目：Positive displacement, helical gear pumps are well suited for pumping oil because

解析：C

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举一反三的答案和解析：

[单选题]With reference to a two-ram actuating mechanism, which one of the following statement is FALSE?

The cross-head is mounted on the rudder stock

[单选题]《中华人民共和国非机动船安全航行暂行规则》中规定，非机动船在航时应给________让路。

所有操纵失灵的船舶