A comparable property sold for $300,000.

In appraisal practice, when adjusting a comparable property to reflect differences from the subject property, the adjustment is always made to the comparable. Since the comparable has a finished basement worth $10,000 and the subject does not, we subtract $10,000 from the comparable's sale price to estimate what it would have sold for if it were more like the subject.

$300,000 − $10,000 = $290,000.

Therefore, the correct answer is A.

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