Answer:
A comma should be placed:
A. after jazz.
Step-by-step explanation:
The sentence in the question is a compound sentence. That means it is formed by two independent clauses. Independent clauses have a subject and a predicate, and they are able to stand alone as a sentence since they convey a complete thought.
To join two independent clauses, we must use a coordinating conjunction. The coordinating conjunctions are: for, and, nor, but, or, yet, and so. However, just adding the conjunction between the clauses is incorrect. We must place a comma before the conjunction. Thus, in the sentence we are analyzing here, the comma must be placed right before "but", or after "jazz":
My uncle loves jazz, but he won't be able to attend the festival.