The correct answer is A) Axe or cutting torch. When towing astern, it is important to have the proper equipment readily available in case the towline needs to be quickly severed. An axe or cutting torch can be used to quickly and safely cut the towline if needed, such as in an emergency situation. This ensures the towing vessel can quickly disengage from the towed vessel if necessary. The other options, while important safety equipment, are not as directly applicable to the task of towing astern and quickly severing the towline. Chafing gear protects the towline, a fire extinguisher is for fire safety, and a first aid kit is for medical emergencies - none of which are as critical as being able to quickly cut the towline if required.