The correct answer is D. VPN.
An open standard is a technical standard that is publicly available and can be implemented by anyone without paying a license fee. Bluetooth, WWW, and HTML are all open standards. VPN
is a private network that is created over a public network, such as the internet. VPNs are not open standards because they are typically proprietary technologies that are owned by a single company or organization.Bluetooth is a short-range wireless technology that allows devices to communicate with each other. It is used in a variety of devices, including smartphones, laptops, and speakers. Bluetooth is an open standard, which means that it is freely available for anyone to use.
The World Wide Web (WWW) is a system of interlinked hypertext documents accessed via the Internet. It is also known as the Web or the Internet. The WWW was invented in 1989 by Tim Berners-Lee at CERN, the European Organization for Nuclear Research. The WWW is an open standard, which means that it is freely available for anyone to use.
HTML is a markup language that is used to create
web pages. It is a standard that is maintained by the World Wide Web Consortium (W3C). HTML is an open standard, which means that it is freely available for anyone to use.A virtual private network (VPN) is a private network that is created over a public network, such as the internet. VPNs are used to provide a secure and private connection between two or more devices. VPNs are not open standards because they are typically proprietary technologies that are owned by a single company or organization.