The correct answer is D) Attempt to call the vessel on VHF radiotelephone because she is disabled. The signal flag "F" indicates that the vessel is "Disabled and requires assistance." According to maritime regulations, when a vessel displays this signal, other vessels should attempt to contact the disabled vessel on VHF radio to offer assistance or determine how they can safely pass by. Stopping instantly (A) or continuing on course (B) would not be the appropriate response, as the disabled vessel may need help or need the other vessel to keep clear (C). Attempting to communicate by radio is the correct action to take in this situation.