不明白地

"The old lady kept bumbling on about something, but nobody could understand her."

"老太太结结巴巴地停,可谁也明白她些什么。"

I really fail to understand what actuated you to give up such a promising post so hastily.

我真明白,什么原因使你这么匆匆地放弃了这样一很有前途的职位。