What natural event typically marks the first day of fall in the Northern Hemisphere?

I work best on a deadline so I start projects close to their due date.

A.) Labor Day

A.) Labor Day

I work on the tasks that I enjoy most first.

B.) The Harvest Moon

B.) The Harvest Moon

I work on the tasks that I enjoy most first.

C.) September Epsilon Perseids (meteor shower)

C.) September Epsilon Perseids (meteor shower)

I work on the tasks that I enjoy most first.

D.) Autumnal Equinox

D.) Autumnal Equinox