99色精品-9色在线-99色在线-99色视频国产欧美日产一区二区三区_亚洲精品亚洲人成在线观看_四虎在线精品永久观看_免费一级a一片久久精

<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