不明白地

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

"老太太结结巴巴地说个不停,可谁也不白她说些。"

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

真不白,原因使你这匆匆地放弃了这样一个很有前途的职位。