What is required for the RAT to recharge the two batteries?

The correct answer involves the necessity of deploying the Ram Air Turbine (RAT) and closing the Bus Tie in order for it to recharge the two batteries. When the RAT is deployed, it generates electrical power from the airflow as the aircraft is in motion, which can be used to recharge the batteries. Closing the Bus Tie allows the electrical power generated by the RAT to be distributed to both battery systems, facilitating their recharging.

In contrast, the other options refer to conditions that do not specifically enable the RAT to charge the batteries. For instance, the Auxiliary Power Unit (APU) being engaged may provide electrical power for various systems, but it is not a requirement for RAT operation. An external power source is also not necessary for the RAT to function, as it operates independently based on airflow. Lastly, the requirement for only battery #2 to be operational does not align with the function of the RAT, which is designed to recharge both batteries when connected appropriately.