Which of the Following Is Correct with Regard to a Contract

Which of the following is correct with regard to a contract entered into with a third person by an agent of an undisclosed principal?

A) The agent has no liability to the third person if the agent has acted within the scope of her authority.
B) The agent is personally liable upon the contract.
C) The undisclosed principal has no liability on the contract, even if her existence and identity are discovered by the third person.
D) If the third party obtains a judgment against the principal and the judgment is satisfied, the agent may still have liability to that third party.