Looking at the answers:

'Remind the controller of his position, if this is possible without interfering with the distress traffic.' --> CORRECT. There is no mention in the question of radio silence having been imposed by the controller. The distress traffic has priority and the pilot of aircraft A should not make a call unless necessary, but in this case, a radio call to remind the controller of their position would be the correct action if it does not interfere.

'Go around and maintain radio silence, as distress traffic has priority over all other traffic.' --> INCORRECT. The distress traffic does have priority but radio silence has not been imposed by ATC. Also, in having an aircraft go-around, this further complicates the traffic situation to be managed by the controller. The question says that the aircraft has been forgotten only, not instructed to remain silent.

'Do the procedure for communications failure.' --> INCORRECT. The aircraft does not have a comms failure.

'Remind the controller of his position, even if it interferes with the distress traffic.' --> INCORRECT. Although radio silence has not been imposed, the pilot on approach should not make a radio call if it interferes with the distress traffic.