The difference between the words swarmed and assembled should give you a clue as to what the answer is. Swarmed means to move somewhere in large numbers, usually crowding around something of interest to get a closer look. Assembled means to gather together in one place for a particular reason. This is usually done in an orderly fashion.
It became a commonplace to say that he was put to death for an error of judgement. Hope This Helps
Answer:
IT'S A.
Explanation: Because an appositive phrase is a noun or noun phrase that renames the noun next to it. And A. is the one that explains about it.