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" :)
Yes a comma can be in any sentence
Hamlet feels that is where a woman has a best chance at being faithful, and where she will cause the least amount of damage. After all, as he tells Ophelia also, "why wouldst thou be a breeder of sinners?"; in a nunnery, she won't have children and bear wicked men-like his uncle-that do awful things.