What is meant by Gross Combination Mass (GCM)?

Answer: A — Powered unit plus trailer plus cargo

The Gross Combination Mass (GCM) refers to the maximum permissible weight of a powered unit, trailer, and cargo combined. This weight is important as it ensures that the vehicle is capable of safely operating with the added weight of a trailer and cargo. Option B is incorrect because it only refers to the weight of the trailer, not the entire combination. Option C is incorrect because it only refers to the weight of the engine, which is not necessarily the same as the powered unit. Option D is incorrect because it only refers to a single vehicle and its load, not the combination of a powered unit, trailer, and cargo. Therefore, the correct answer is A.