A chemist has 500 mL of a 30% acid solution. She adds x milliliters of a 10% acid solution. Which statement is true about the graph of the function that represents the concentration of the final solution?

The mixture contains 150 mL of acid initially, and adding x mL of 10% solution adds 0.1x mL of acid. Its concentration is 100(150 + 0.1x)/(500 + x) percent, which approaches 10% as x grows. For every finite x ≥ 0, the original 30% solution keeps the final concentration greater than 10%, so choice B is true.

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