The answer to that can be found in the FAQ.
Ok.. here's what the faq says:
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It says my answer is wrong...What should I do?
Then it's wrong and you just have to keep trying. But remember, the solution is case-sensitive. If you are absolutely sure you've got the right answer, be sure to try all the reasonable possibilities of that answer.
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So what part of this is answering my question? It tells me what to do when I think I have the answer, but it doesn't answer why are the solutions case sensitive? Lazyness?