Final answer:
The BEST data to use when estimating the market value of a fifteen-year-old house is recent sales of comparable properties.
Step-by-step explanation:
The BEST data to use when estimating the market value of a fifteen-year-old house is d. Recent sales of comparable properties. This is because recent sales of similar properties in the same area provide an indication of the current market value. By comparing the prices at which similar houses were sold, one can get a better estimate of the value of the fifteen-year-old house. Other options, such as the owner's original cost, the offering price in the listing, or the owner's best estimate of the value, may not accurately reflect the current market conditions.