In the arts (and in business), there's a classic theory that the best things happen at the convergence of disciplines. You develop immunity to the "paradox of expertise" when you have a large knowledge base, where your advanced knowledge of one area clouds your ability to see new ideas.
The answer is B. "The coffee shop was usually full" and "Today there were many open tables" are both independent clauses joined together with the coordinating conjunction "but" :)
