单选题The valve that prevents water from backing out of the boiler into the feed line is the（）.Abottom-blow valveBskin valveCfeed-check valveDfeed-stop valve
单选题
The valve that prevents water from backing out of the boiler into the feed line is the（）.
A
bottom-blow valve
B
skin valve
C
feed-check valve
D
feed-stop valve
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