As for this problem about the part of the Internet, the most probable and the most likely to be the answer out of the options presented together with the problem is A. Interface.
Interface would be the part of the Internet that you typically see. Interface is the widely known term used for GUI or Graphics User Interface. This covers about as to how you handle your desktop or computer. Basically, the moment the browser is opened, the interface appears. The other options are also arguable and that they might also pose the possibility of them being the correct answer taken as they are. Interface would cover them all and be the most likely answer.
