\textbf{97 --} \textbf{A mixture of $a$ milliliters of strong acid solution HA ($\mathrm{pH=1/4}$) and $b$ milliliters of the same acid solution ($\mathrm{pH=1/7}$) with 200 milliliters of 0.3 molar sodium hydroxide solution becomes neutralized. $a+b$ equals how many milliliters?}
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(1) 500 \quad (2) 1000 \quad (3) 250 \quad (4) 2000
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