The correct answer is C) the bottom of the lube oil sump. In a bypass type lubrication system for a diesel engine, the dirty oil line to the centrifuge should be taken from the bottom of the lube oil sump. This is because the oil at the bottom of the sump contains the highest concentration of contaminants and sludge, which need to be removed by the centrifuge to keep the engine lubrication system clean. The other options are incorrect because: A) the lube oil pump suction line would not have the highest concentration of contaminants, B) the lube oil pump discharge line is already under pressure and does not need to be drawn from, and D) the outlet from the lube oil header is already filtered and does not require further cleaning.