The correct answer is A) The drains from lube oil coolers can be directed back to the main sump, the sludge tank or the lube oil purifier. This is the correct answer because the lube oil system is designed to recirculate and reuse the lubricating oil, and the drains from the coolers allow the oil to be routed back to the main sump, sludge tank, or purifier for cleaning and reuse. The other options are incorrect because: B) the gravity tank overflow does not directly go to the sludge tank, C) the gravity tank does not directly supply the turbines and gears, and D) the temperature control valve regulates the cooling water flow to maintain the desired oil temperature, not bypass the cooler entirely.