Answer: Even though the brain makes up only two percent of you're total body weight, it uses up twenty-five percent of the body's supply of oxygen.
Explanation: "You're" should be switched to "your" because you're means you are but put together. The sentence would be rewritten as this:
Even though the brain makes up only two percent of your total body weight, it uses up twenty-five percent of the body's supply of oxygen.
Therefore, select "you're" for your question.
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