Final answer:
Trailer ratings are primarily based on the total weight of the trailer and boat.
Step-by-step explanation:
Trailer ratings are based on the total weight of the trailer and boat (option c). The weight of the trailer and boat determines how much weight the trailer can safely carry. Different trailers have different weight capacities, and it is important to match the trailer rating with the weight of the boat to ensure safe transportation. Other factors such as length and width of the trailer, type of boat, and type of hitch may also play a role in the trailer rating, but the total weight is the primary factor.