The bilge system has been performing well; however, the aft starboard engine room bilgewell suddenly fails to be pumped outWhich of the following should be done first to determine the cause?（）
- AOpen the bilge pump for inspection
- BRemove each of the manifold valves
- CRemove only the manifold valve to the affected bilge-well
- DAttempt to pump out another bilge well to determine if the entire system is affected