The correct answer is based on the standard measurement used in roofing to quantify the coverage of shingles. A "square" of roofing material, specifically asphalt shingles, is defined as covering an area of 100 square feet.
When examining the dimensions for coverage, a square that measures 10 feet on each side would have an area calculated as follows: 10 feet x 10 feet = 100 square feet. This aligns perfectly with the definition of a square in roofing terms, making it the correct answer.
The other dimensions would result in areas that either do not meet this standard or exceed it. For example, the 5 x 5 square covers only 25 square feet, while the 12 x 12 square would cover 144 square feet, and a 15 x 15 square would cover 225 square feet. None of these options fits the standard roofing measurement of a square correctly, reinforcing that the 10 x 10 dimension accurately represents what is meant by a square of asphalt shingles in roofing practice.