Rules of the Road: BOTH INTERNATIONAL & INLAND Which statement is TRUE concerning fog signals?

I can agree with Walker2016 but, the Rules do state that a pilot vessel SHALL sound the same as a power driven vessel in fog but MAY IDENTIFY themselves as a pilot. So, as I read into answer (D) the identity signal of 4 short is not considered the fog signal rather, the Prolonged blasts preceeding it is. Very tricky, I did have to think on this hard.

Four short blasts is not the only fog signal sounded by a pilot vessel. It may sound four short when engaged in pilotage duty but it not always engaged in pilotage duty.

Vessel aground is authorized under rule 35h that it can sound an 'appropriate signal' but doesn't specify what that is. Some USCG study material on their site suggest ICS 102 signals as what they are discussing in this rule.