Rules of the Road: BOTH INTERNATIONAL & INLAND Which vessel may sound the danger signal?

Rule 34(d) When vessels in sight of one another are approaching each other and from any cause either vessel fails to understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by giving at least five short and rapid blasts on the whistle. Such signal may be supplemented by at least five short and rapid flashes.

David,

Your confusing this with a vessel anchored in restricted visibility. There is no reference to restricted visibility in this question. All of the choices are vessels in sight of each other, which is a requirement for the danger signal.