What device is responsible for transmitting data between different networks?

A router is the device responsible for transmitting data between different networks. Its primary function is to determine the best path for data to travel between various networks, ensuring that data packets are effectively directed towards their destinations. Routers operate at the network layer of the OSI model, using IP addresses to route data accurately.

While modems are used to modulate and demodulate signals for internet connectivity, and switches facilitate communication within a single network by connecting devices, a router's role transcends these functions. Bridges also connect and filter traffic within a single network but do not manage the transmission between multiple networks. Thus, the router's capability to interface and direct traffic across disparate networks makes it the correct answer.