单项选择题 Fuel oil tanks must be fitted with （） that can be closed rapidly and remotely in the event of an emergency such as a fire.

单项选择题 A more sophisticated pressure reducing valve incorporates a pilot valve which controls the fluid above the valve operating piston in response to downstream pressureThe bold and italic word “which” means （）.

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