A computer typically connects to a router via a _______.

A computer typically connects to a router via a network interface card (NIC). This card serves as the hardware interface between a computer and a network, allowing it to communicate over a local area network (LAN) or the internet. The NIC can use various physical connection methods, such as Ethernet cables for wired connections or wireless signals for Wi-Fi, to establish communication with the router.

The reason the other options do not apply is that a USB port is generally used for connecting peripheral devices rather than networking directly. A power extension is designed to provide additional electrical outlets; it does not facilitate network connectivity. An HDMI cable is used primarily for transmitting video and audio signals, making it unsuitable for connecting to a router for data communications.