Why will a set of stars appear at a different angle to us at different times of the year?
a. because we change location as earth orbits the sun
b. because the stars move back and forth across the sky
c. because of distortions by gravity

A. because we change location as Earth orbits the sun

Explanation:

We have to remember that the universe is traveling and expanding and we are all traveling along with it, in this case the stars are expanding and traveling with the universe along with us, but the appearing on a different angle to us on different times of the year is because we orbit the sun, changing the angle at which we see the stars.