The correct answer is b. The verb tenses shift.
This is because the tenses don't match, meaning that at first you have a present simple and then a past simple. In order for them to be consistent they should be in the same tense.
Answer: tone
In any kind of formal writing, the writer should be sure to use formal tone, or attitude, toward the subject.
Answer:
The biggest difference between high school and university is that you're treated as an adult. ... That means you get to take greater control of how you spend your time and what you study. It also means that your education is your responsibility, no one is going to do it for you.