What documents must be present in the glider during flight?

The correct answer includes essential documents that are specifically required to ensure the glider is in compliance with regulatory standards and to support safe flight operations. The airworthiness certificate demonstrates that the glider meets safety and design standards set by aviation regulatory authorities, confirming it is in a condition for safe operation.

Registration is also crucial as it provides legal identification for the aircraft, allowing authorities to track ownership and compliance with regulations. The operator's manual contains specific information needed for the safe operation of the glider, detailing important procedures, limitations, and maintenance requirements. Lastly, the weight and balance documentation is critical in ensuring that the glider is loaded correctly, which affects flight performance and safety.

These documents collectively ensure that the flight operations can be conducted safely and in accordance with applicable regulations, thus making this set of documents the correct answer for what must be present in the glider during flight.