The correct answer is B) Attempt to pump out another bilge well to determine if the entire system is affected. The reasoning behind this is that if only the aft starboard engine room bilge well is failing to be pumped out, it indicates a problem specific to that well rather than the entire bilge system. Attempting to pump out another bilge well will help determine if the issue is isolated or affects the entire system. This is the logical first step to diagnose the problem before taking more intrusive actions like opening the bilge pump or removing manifold valves. The other options are incorrect because opening the bilge pump for inspection (A) or removing the manifold valves (C, D) are more involved troubleshooting steps that should only be taken if the initial test of another bilge well indicates a broader system issue.