The correct answer is (c), Intranet.
An intranet is a private network that uses Internet technologies and protocols to share information, applications, and computing services within a limited group of users. Intranets are typically used by businesses, government agencies, and educational institutions to share information and collaborate on projects.
Video conferencing, email, and browsing the web are all applications of the internet. Video conferencing allows users to communicate with each other in real time using video and audio. Email is a way to send and receive messages electronically. Browsing the web is the process of accessing and viewing information on the World Wide Web.
Intranets are not applications of the internet because they are not accessible to the public. Intranets are private networks that are only accessible to authorized users.