All of the above is the correct option.
The first option,
One thing that will help you, Katie, is to place all of your assignment due dates in a planner, or on a calendar.
You're, because it is a homphone (you're, your) and makes sense in this sentence.
Answer:
Ethos is a writer's ability to build credibility, establish himself as an expert, and/or convince the readers that he has their best interests at heart.
Explanation: