The correct answer is A) fundamental.
The word that conveys the connotative meaning of the word primordial in this context is fundamental.
When we find the phrase in the excerpt that says "the dog is primordial," this means that the dog is of the utmost importance, or that without the dog, the sleds cannot function. Primordial is a word that means absolutely necessary. So you use it when you try to refer to something indispensable.
