单项选择题

The piston rings if found worn out （） and supplied by shipchandler.

A.must replace
B.must to be equipped
C.has to be repaired
D.have to be renewed

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单项选择题

A.larger than
B.smaller than
C.equal to
D.none of the above

单项选择题

A.chromium-plate against wear
B.anti-corrosion treated
C.white metal lined against wear
D.flame hardened against wear

单项选择题

A.to revolve
B.revolved
C.revolving
D.to be revolved