The experts couldn't reach any consensus on the cause of the illness.
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history
From the late-Qing novel《痛史》by Wu Jianren: 议论纷纷，莫衷一是 — the generals could not agree whether to defend, fight to the death, or flee. The chengyu has become standard for committee deadlock.
grammar
莫 = 'no one'; 衷 = 'to settle on'; 一是 = 'a single right answer.' Literally 'no one settles on the one right.' Use as a predicate after 对 + topic, or as a finishing comment.
