The correct answer is A) pump suction line. A coarse screen wire mesh strainer is typically found on the pump suction line of a diesel engine lubrication system. This strainer helps to prevent large debris or contaminants from entering the lubrication pump, which could otherwise cause damage to the pump or other components in the system. The other answer choices are incorrect because: B) The filter bypass return line would not normally have a coarse strainer, as this line is designed to bypass the primary filter. C) The pump discharge line would not typically have a coarse strainer, as the pump has already drawn the oil through the suction strainer. D) The gravity tank inlet line would not have a coarse strainer, as the tank is designed to receive the pre-filtered oil from the lubrication system.