Prices of commercial lots (land that can be developed for business purposes) in a particular large county follow a normal distribution with an unknown mean and a standard deviation of $10,000. A large real estate company in this county is interested in buying and developing commercial lots that sell for $15,000 below the mean or lower. What proportion of lots will this company buy? Choose the answer closest to your calculations.

A.7%
B.10%
C.50%
D.This question cannot be answered as the normal distribution does not have a known mean value
E.93%