This is called a folder
(a) collapsing
(b) expanding
(c) displaying​

What is domain name system (dns)? allows dynamic ip address allocation so users do not have to have a preconfigured ip address to use the network converts ip addresses into domains, or identifying labels that use a variety of recognizable naming conventions the efficient coexistence of telephone, video, and data communication within a single network, offering convenience and flexibility not possible with separate infrastructures the integration of communication channels into a single service