题目内容

Gearpumpsarefixeddisplacementpumps.

A. 对
B. 错

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Crescentgearpumpsarevariabledisplacementpumps.

A. 对
B. 错

Somegearpumpsarevariabledisplacementpumps.

A. 对
B. 错

Many people have hobbies. They make things or _____ things. Right now, someone is enjoying a hobby somewhere. People collect _____, rocks, records, pictures, or china. Some people like to make ______. They could make a table, a chair or a boat, or make a cake, an apple pie or some ice cream. People with hobbies are not _____. They are interested in their hobbies because they can _____ their leisure activities. Some work and some play will make people interested, too.

Whatistheadvantageofexternalgearpumps?

A. reliableperformance
B. simpleconstruction
C. lowcostofproduction
D. alloftheabove

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