in fall ,在秋季,表示泛指。

例句

The study also found that those born in fall less probably had a mood of depression which may easily drive them to cry, while those in winter were not easier to be angry.

这项研究还发现,出生在秋季的人不大可能出现容易让他们哭泣的抑郁情绪,而冬天出生的人则没那么容易生气。

in the fall 在秋天在秋季坠落走马灯表示具体的某一个秋天。

例句

He has designed to go to Australia for a trip in the fall.

他已经打算秋天去澳大利亚旅行。