Select the correctly punctuated sentence. Select one:
a. School began on a cold September morning.
b. School began on a cold, September morning.
c. School began on a cold September, morning.
d. School began on a cold, September, morning.

Aman lives on the twelfth floor of an apartment building. every morning he takes the elevator down to the lobby and leaves the building. in the evening, he gets into the elevator, and, if there is someone else in the elevator -- or if it was raining that day -- he goes back to his floor directly. otherwise, he goes to the tenth floor and walks up two flights of stairs to his apartment.