---from his accent,he ---be from Shanghai.

A
judging from/by 由.判断,judging from 用作独立结构,即不用考虑从句和主句逻辑关系的一致性,用法相当与：generally speaking,considering (考虑到）e.g.:judging from the truth,he is honest enough.
另外 判断句中
肯定判断用must be
否定判断用can't be