Question

the is an article, but its capitalized because its the first word in the title.
in this title, on isnt capitalized because its a preposition.
which is the correct version of the title below?
my teacher read us the poem stopping by woods on a snowy evening by robert frost.
\stopping by woods on a snowy evening\
\stopping by woods on a snowy evening\

Explanation:

In title - case, the first word is capitalized. Also, prepositions are usually not capitalized. "Stopping" is the first word so it should be capitalized. "On" is a preposition and should not be capitalized. Nouns like "Woods", "Evening" and adjectives like "Snowy" should be capitalized.

Answer:

"Stopping by Woods on a Snowy Evening"