The correct answer is A) Shift pump suction to an alternate settling tank. When water is found in the fuel oil settling tank, the first action that should be taken is to shift the pump suction to an alternate settling tank. This is because continuing to draw fuel from a tank with water contamination could lead to potential engine issues or damage. Shifting to an alternate tank allows the crew to isolate the contaminated tank and investigate the extent of the issue before resuming normal fuel system operations. The other options, while potentially useful, should be considered as secondary actions after the suction has been shifted to a clean tank.