Which of the following is an example of an auxiliary station?

In amateur radio, an auxiliary station is specifically defined by the FCC as a station that transmits point-to-point within a system of cooperating stations. A classic example is a "link" station that sends audio from a remote receiver site back to a main repeater transmitter. Because remote receivers are often placed in distant locations to improve a repeater's listening range, they need a dedicated radio link (an auxiliary station) to send the received audio back to the main transmitter. This one-way control/link transmission is the exact purpose of an auxiliary station. The term "auxiliary" in everyday English might sound like a "backup" radio for emergencies or contests, but in Part 97 rules, it refers exclusively to these specific system-linking operations. It is also completely distinct from the Military Auxiliary Radio System (MARS).