Answer:
correct option is D) Whistle only
Step-by-step explanation:
solution
equipment for fog signals is Whistle only because according to rule 33 of Equipment for Sound Signals
as length 12 meter or more than 12 meter there need only a whistle
and when length is more than 20 meter than bell in addition required with whistle
and length 100 meter or more than gong is additional provided with bell and whistle
so here
correct option is D) Whistle only