falter|faltered|faltering

她的声音开始颤抖，几乎说不出话来。

Her voice began to ___falter as she tried to speak.

老人在结冰的人行道上蹒跚而行。

The old man ___faltered on the icy sidewalk.

他说话结结巴巴的，因为太紧张了。

He spoke with a ___faltering voice because of nervousness.