Chuck tells his son Jeff that it's complicated to explain what a muscle car is but chuck says the best example of a muscle car from the 1960s is the mustang chuck has explained this concept of the muscle car basing on using the

prototype model

Explanation:

Given that in mechanical engineering, a prototype model of a product or car is a product version, often not a complete type or version that still needs some adjustment or comes in a lower but nonoperating version, yet has virtually all the physical features of the actual or final version of that product.

Hence, in this case, though Chuck has admitted it is difficult to explain what a muscle car is, he has explained this concept of the muscle car basing on using the "PROTOTYPE MODEL"

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