单项选择题
You should frequently compare drum-mounted and remote-reading water level indicators（） between these have contributed to failures because of overheating through shortage of water, when a boiler was being oil-fired.
A.descriptions B.discrepancies C.different D.deflections
单项选择题 The safety valves should be tested and adjusted when the boiler survey is （）
单项选择题 A donkey boiler is （）.
单项选择题 Safety valves on a boiler vent to the （）.
