[单选题]活塞环黏着在环槽中将导致______。

正确答案 ：A

密封不良

[单选题]If a reciprocating air compressor has a knock occurring in frequency with its operating RPM, the cause is probably _____.

正确答案 ：A

misalignment or worn main bearings

[单选题]在火场进行防护时，应做到以下几点：

正确答案 ：D

以上都是

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