The moving part of the valve is a ______(铜环) with _____(凹槽) arou

The moving part of the valve is a ______(铜环) with _____(凹槽) around the outer perimeter and 3 holes drilled fore and aft.

A.O ring, menber;

B.bronze ring, lug;

C.grooves, chamber;

D.bronze ring,groove;

正确答案是D