Select the most appropriate option to fill in the blanks.
We have four seasons because the earth doesn't sit up straight; it's ______ on its axis. As it orbits the sun, the planet's slight slouch ______ more or less of the northern and southern hemisphere to the sun depending on the time of the year.

* For the first blank, "tilted" is the scientifically and contextually accurate term to describe the earth's position relative to its axis (tilted on its axis).
For the second blank, the subject is "the planet's slight slouch," which is singular. Therefore, it requires a singular verb (exposes).

Option B satisfies both context and grammatical subject-verb agreement perfectly.