97免费在线观看视频,亚洲综合自拍网,黄色毛片免费观看,热久久综合网,免费看日产一区二区三区 狠狠操av,久久久涩涩涩,在线精品免费视频,人人插天天干,久久91精品国产91久久

單項選擇題

Cocks and valves control or interrupt flow, and have internal passages arranged so that they can be restricted or closed: in cocks, by rotating the plug, and in valves, by lowering, raising or rotating a disc in relation to a seating surfaceAccording to the above sentence, which of the following statements is not true?()

A.Flows of fluids can be restricted by both cocks and valves
B.There are seats in the internal passages of valves
C.A disc of valve only moves up and down
D.We can infer that there is a bore in cock ping

微信掃碼免費(fèi)搜題