The correct answer is C. Handoff.
A handoff is the process of transferring a mobile station from one base station to another during a call. This is necessary when the mobile station moves out of range of one base station and into the range of another. The handoff is performed by the mobile switching center (MSC), which is the central office in a cellular network. The MSC coordinates the handoff between the two base stations and ensures that the call is not interrupted.
A roamer is a mobile station that is not registered with the home network. This can happen when the mobile station is traveling outside of its home area. When a roamer makes a call, the call is routed through the home network and then to the visited network. The visited network is the network that the roamer is currently using.
A forward channel is a channel that is used to transmit data from the base station to the mobile station. The forward channel is used for voice calls, data calls, and text messages.
A mobile switching center (MSC) is a central office in a cellular network. The MSC is responsible for routing calls, managing handoffs, and providing other services to mobile stations.