Explanation:

Accessories, also known as peripheral devices (e.g., mouse, keyboard, printer, external hard drive), connect to the computer's system unit through "Ports." A port is a physical interface on the computer that allows data to be exchanged with external devices. Option (b) "Ring" refers to a network topology where devices are connected in a circular fashion, not a physical connection point for accessories. Option (c) "Bus" refers to internal communication pathways within the computer, not external connection points. Option (d) "Zip" could refer to a file compression format or an older type of removable storage drive, neither of which is a general connection point for accessories. Thus, (a) Port is the correct answer.