单项选择题 A pumproom is suspected of accumulating gases after a ventilation machinery breakdown. Where should the combustible gas indicator case be placed when testing the pumproom atmosphere for combustible gases? （）

单项选择题 A psychrometer has two thermometers that provide dry bulb and wet bulb temperatures. By comparing these two temperature readings with a set of tables you can determine the （）.

单项选择题 A predictable result of a vessel nearing a bank or edge of a channel is that the（）.