When the control operator is not the station licensee, who is responsible for the proper operation of the station?

The FCC explicitly states that both the station licensee and the control operator are jointly responsible for the proper operation of the station. This means both parties share the liability for any rule violations. If you let a friend use your radio and they break a rule, you as the station licensee are held responsible for allowing it, while they are responsible as the control operator. Options stating that 'only' one or the other is responsible are incorrect because accountability is always shared.