单项选择题 In a complete oil/water separator, more oil will separate out onto the underside of these plates and travel outwards until it is free to rise into the oil collecting space Whats the meaning of "it" in the sentence above?（）

单项选择题 In a commonly used fuel oil system, the oil is stored in tanks in the double bottom from which it is pumped to （） and heated.

单项选择题 In a central cooling system, used in some modem ships, sea water is supplied to cool （）which will circulate to other individual cooler, greatly reducing the corrosion problems.