As a writer I find it hard sometimes to write unrestricted. I often feel as though I need to appeal to someone. This quote is very nice to hear because it kind of relaxes that thought of needing to be something instead of just being myself through my writing.
A warrant is an underlying assumption or inference that the writer takes for granted.
The best thesis statement would be:
A. Schools should encourage volunteering because it reduces stress, promotes personal growth, and has a positive effect on society.
This is the best because it provides the topic "Schools should encourage volunteering" and then it goes on to provide reasons for this that will most likely be described in the rest of the paper.
Hope this helps!