Question

Planet C has a tilt of zero degrees. What seasonal changes would be expected on this planet?

Answer 1

The second statement is your answer:

 No change in temperatures between seasons. Since tilt is the angle between the direction of positive pole and the normal to the orbital plane, seasons occur due to the tilt of axis. If there were to be no, or zero degree tilt, then there will be no season because of the lack in temperature changes. The amount of sunlight received remains same throughout the year which results in no temperature change 

Answer 2

"Tilt of zero degrees" means the planet's rotation axis is "straight up and down".

...  No place on the planet has any seasons.
...  The climate at every place is the same all year around.
...  No place on the planet has any changes in the length of its days.
...  Every place on the planet has 50% light and 50% dark, every day.
...  At the poles, the sun goes around and around and around the horizon.