单项选择题 A(n) （） is a special type of valve which prevents the passage of steam but allows condensate to pass.

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 （）.