To accurately identify the phrase that best supports an answer to Part A, I would need to understand the specific question or answer from Part A regarding "close calls in U.S. election history."
However, if the focus is on a phrase indicating a controversy or the potential for disputes in election results, then option A, "This sparked major controversy" (Paragraph 13), would be the most supportive. If Part A's answer pertains to procedural aspects of recounting votes, then option C, "a mandatory recount" (Paragraph 14), could be the best fit.
Please clarify the answer or context of Part A for a more precise response!