Question

Select the correctly punctuated sentence.

School began on a cold September morning.
School began on a cold, September morning.
School began on a cold September, morning.
School began on a cold, September, morning.

Answer 1

School began on a cold, September morning.

Answer 2

Comma right after cold

Answer 3

^Yep, and there is no comma necessary before the object 'morning' ~
Therefore the second option is correct :D