This very much depends on your school, but a common rule for most is that you must pass all of your classes no matter what you choose.
In some states there are state tests you must pass to graduate as well. For me, I had to take an Algebra State Test to pass 9th and continue.
Definitely cell phone reception! However books could be argued for since they also are a good more than a necessity. However the last 2 i believe would be classified more as necessities than goods.
~Hope this helps!~
The answer is the table of contents because it tells you where to find every lesson that is in the book
