Which type of network is exclusively used to connect computers within a single company?

The choice of an intranet as the correct answer is grounded in its primary function within a company. An intranet is a private network designed to facilitate communication, collaboration, and the sharing of information among employees within an organization. It is accessible only to members of the organization, enabling the secure exchange of data, resources, and applications that are specific to that company's internal operations.

In contrast, an extranet extends certain aspects of an intranet out to authorized outside users, partners, or customers, enabling them to access specific resources while maintaining a level of security. A LAN (Local Area Network) also connects computers within a limited geographic area, like a single building or campus, but it does not define the confidentiality or the intent of the network usage as specifically as an intranet does. A VPN (Virtual Private Network) provides secure remote access to private networks over the internet, allowing users to connect from external locations, which further distinguishes it from the singular purpose of an intranet.

Thus, an intranet's defined role as an internal network for a company's employees is what makes it the most fitting answer to the question of which type of network is exclusively used to connect computers within a single company.