Richard Writes a Letter to Sarah Authorizing Her to Sell

Richard writes a letter to Sarah authorizing her to sell his car and sends a copy of the letter to Timothy, a prospective purchaser. The next day, Richard sends a letter to Sarah revoking her authority, but he fails to notify Timothy. Sarah:

A) has actual authority to sell the car to Timothy.
B) has implied authority to sell the car to Timothy.
C) has apparent authority with respect to Timothy to sell the car.
D) is empowered under the doctrine of respondeat superior to negotiate the contract.