When may an amateur station transmit without a control operator?

The correct answer is when the station is operating with automatic control, such as in the case of a repeater. In this context, automatic control means that the station is designed to operate without a human operator present, typically enabling it to accept and respond to incoming signals autonomously. This is common practice for repeaters, which are set up to extend communication range by receiving, amplifying, and retransmitting signals without needing constant supervision.

In contrast, the concept that an amateur station should never transmit without a control operator means that for any operation not involving automatic control, a licensed operator must be present to ensure compliance with regulations and proper operation of the station. This ensures that there is accountability for the transmissions and adherence to the amateur radio rules.

Thus, while the other options present scenarios where a licensed amateur might be using the station or imply different types of operation, they do not satisfy the regulations governing amateur radio operations that emphasize the necessary oversight by a licensed control operator at all times unless automatic control is in effect.