While trying to learn what a "dog" is, Arash mentally compares every animal to his family's new puppy. If the animal is similar enough, he decides that it is also a dog. Arash's puppy serves as a for the concept of "dog."
A) proposition
B) heuristic
C) concept
D) prototype

D. Prototype

Explanation: A prototype could be seen as a canvas, design or knowledge upon which future designs or knowledge patterns are based. It could be the original version of something or object upon which future development or concept related to such objects are based.

In the scenario above, Arash uses his family's new puppy as a prototype in his bid to learn what a 'dog' is by mentally comparing any animal to the puppy. The puppy was used as a basis for developing the knowledge of what a dog is.