you can find all the answers in the back of the book
<span>The sentence that uses a contraction or possessive form incorrectly is A. I can't believe your going to be in high school next year. The mistake here is the word your - it should be you're, because that is short for you are, and your is a pronoun denoting possession: your cat, your dog, but You're wrong, meaning You are wrong.The remaining sentences have no mistakes in them. </span>
Answer: Simply because he believes that someone has to fight for Tom, and no one else would do it.
Explanation:
Atticus was not only defending Tom Robinson in the case, but also against all the racist people who believed he was guilty just because he had coloured skin. Atticus was trying to show her daughter that some causes, though lost, should be defended.