Given a text T, and several options, according to the question posed in the text T to choose the most appropriate option from the options as the answer, please directly output the most appropriate option, do not need to output the explanation.

What is the most significant drawback of a repeat sales index to measure returns to real estate?
Option A:Sample selection bias
Option B:Understatement of volatility
Option C:Reliance on subjective appraisals

Answer: A