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The ampacity rating of a cable supplying a dwelling unit range receptacle is determined by the requirements outlined in the National Electrical Code (NEC) and depends on the nature of the load and the type of circuit protection used. In this case, with a 60/75°C breaker, the ampacity for conductors, depending on their insulation type, varies.

For a typical dwelling unit range, which is considered a continuous load, the NEC generally requires that the circuit be rated at 1.25 times the continuous load. In residential applications, a common practice is to use 40A circuit protection specifically for ranges.

When a cable is rated for 40A, it means that the conductors used in that cable can safely carry the load without overheating, as long as they are suitable for connection to a 40A breaker. The conductor's ampacity is also referenced at the temperature ratings of the insulation, which in this case, refers to the lower ratings of 60°C or 75°C. The ampacity corresponding to these ratings for the right conductor gauge will fall within the 40A category.

Therefore, the correct answer is the 40 A rating, which not only adheres to code requirements but also ensures safe and