対立

両社の意見が ___ し、交渉は決裂した。

The correct answer is 「対立」(たいりつ), meaning "opposition," "confrontation," or "conflict." The phrase "交渉は決裂した" (negotiations broke down) indicates a failure to reach an agreement, which is a direct consequence of the opinions of both companies being in conflict. 「一致」(いっち) means "agreement" or "unanimity"; if opinions agreed, negotiations would not break down. 「統合」(とうごう) means "integration" or "unification"; while integrating opinions might be a goal, if it leads to breakdown, it's not a direct description of conflict. 「妥協」(だきょう) means "compromise"; a compromise is an outcome of negotiation, but if negotiations break down, it means compromise was not achieved.

正解は「対立（たいりつ）」です。「両社の意見が対立し」、つまり「意見が食い違い、ぶつかり合った」結果、交渉が決裂した、という流れが自然です。「一致」は意見が合うこと、「統合」は一つにまとめること、「妥協」は譲り合うことで、いずれも「交渉決裂」とは結びつきません。