单项选择题
（） may be fitted for operating the derrick topping lift (the wire which adjusts the derrick height).
A.A capstan B.A hold C.A warp end D.A mooring drum
单项选择题 （） provides the head or pressure to supply the domestic water where required.
单项选择题 Under rotary pumps are the gear, （）, cam-and-piston and screw types.
单项选择题 The water level in the gauge glass when a boiler is operating is （） when the boiler is shut down.
