无码高清视频|成人自拍视频|欧美成人午夜无码A片秀色直播|草美女视频网站|美女被操网站在线观看

<em id="sae9p"></em>

單項(xiàng)選擇題

In its simplest form the pressure reducing valve is opened or closed by （） which is balanced by the downstream pressure acting on a diaphragm.

A.adjusting a nut
B.a pre-tensioned spring
C.any spring
D.upstream pressure

你可能感興趣的試題

單項(xiàng)選擇題

Most marine biological sewage treatment plants consist of all the following statements except （）.

A.aeration tanks
B.settling tanks
C.disinfection agent
D.anaerobic bacteria

單項(xiàng)選擇題

To prevent accidents from occurring, special valve chests are used in such cases in which interchangeable blanks and connecting passages are incorporatedThe bold and italic word “which” means （）.

A.accidents
B.special valve chests
C.interchangeable blanks
D.connecting passages