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答案：A
解析：
Option A is correct. If x represents the uniform width, in feet, of the patio then (15+2x)(30+2x) represents the total area, in square feet, of the patio and pool combined. The problem states that this is equal to 800 square feet, so (15+2x)(30+2x)=800. This equation can be rewritten as (2x-7)(x+25)=0 and solved for the positive value of x.
