Which type of cable connects external modems and routers in some laptops?

The correct choice highlights the use of a serial cable, specifically the DB9 type, which historically connects external modems and routers to laptops. This type of connection was common in earlier computing environments, particularly before the widespread adoption of USB and Ethernet technologies.

In the context of connecting to external modems, the DB9 serial cable facilitated communication by providing a direct wired interface for data transfer, following the RS-232 standard. This allowed for a reliable point-to-point connection between devices, which was essential in scenarios involving dial-up modems.

USB-C cables, while versatile and increasingly common for newer devices, are more typically used for charging, audio/video transmission, and data transfer in modern technology but do not traditionally serve the specific purpose of connecting external modems and routers in older laptop models. Similarly, HDMI cables are designed primarily for high-definition audio and video transfer and are not used for networking purposes, while Ethernet cables are primarily used for local area networking rather than direct connections to modems or routers on older systems. Therefore, in contexts where an external modem connection is involved, the DB9 serial cable remains relevant for its designated purpose.