The answer is A. spectators'. Because the apostrophe after the "s" means there are more than one.<span />
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!
It was written on the year 2011
