问题描述：
[单选]
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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答案解析：无
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答案解析：无
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上一篇：The piston supporting body is mainly subjected to（）stress．
下一篇：The piston rings are manufactured with a diameter（）the bore of the cylinder．
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