His courage ________as the two of them continued to stare at him, each daring him to go on.
句意: 当他们两个继续盯着他看的时候, 他的勇气开始动摇, 每个人都鼓励他继续前进。 waver动摇(信念; 决心) 。 swing摇摆; 挥舞。 fluctuate波动;动摇。 vibrate震动; 颤动。