In an Agency to Sell Real Property Which of the Following

In an agency to sell real property which of the following renders the authority and contract of sale valid?

A) General power of attorney, granting the agent authority to sell real property, not put into writing.
B) General power of authority put into writing without authority to sell.
C) A special power of attorney put into writing authorizing the agent to sell real property of the principal.
D) Special power of attorney couched in general terms without referring to specific acts of dominion.