Which of the following devices relies on a network for communication?

The choice that indicates a device relying on a network for communication is a desktop computer connected to a router. A desktop computer connected to a router is designed to send and receive data over a network, enabling online communication and access to internet resources. This connection to a router allows the desktop to interact with other networked devices, reach external networks, and access shared resources such as files and printers over the local area network (LAN) or the internet.

In contrast, the other devices listed do not primarily rely on a network for their fundamental operations. A scanner, while it can be network-capable, typically functions independently or uses a direct connection to a computer for scanning documents. A standalone printer operates independently without any network dependency, handling print jobs directly from connected devices, such as computers via USB. Similarly, a USB flash drive is a portable storage medium that does not utilize a network for its operation, as it connects directly to a computer's USB port to transfer data.