Assertion (A) is correct: In communication theory (J. Paul Leagans), channels are defined precisely as the physical bridges, conduits, or pathways that join the communicator and the receiver, enabling messages to travel between them.
Reason (R) is correct and explains (A): Leagans and Berlo defined three operational dimensions that constitute a communication channel: (a) Mode of encoding/decoding (speaking, writing, gesturing), (b) Message vehicles (spoken words, printed pages, electrical signals), and (c) Vehicle carriers (air waves, telephone wires, postal system, radio transmitters). Because these vehicles and carriers physically carry the encoded content across space, they function as physical bridges between sender and receiver.