Answer:
a. Performance of the contract by the agent.
Step-by-step explanation:
After validly contracting with an agent representing an undisclosed principal, the third party is entitled to the performance of the contract by the agent. The agent is liable to carryout the contract.
Option B is wrong since the contract has been identified as valid by the third party, there is no need for ratification of the contract.
Option C is also incorrect because the agent is under no obligation to disclose the principal.
Option D is also incorrect because the third party does not have the power to void a contract merely because he/she is not comfortable with the principal.