This is a bit of an odd question, my phone contains hardware, software, data, and allows the option of users. Mainframe, and Node can mean a lot of things, so I assume it's not that. When they say Computer System, I always think of my Windows computer at first, but even Computer System could reference something like a server computer. A Computer System could even mean something like a whole bunch of terminals connecting to a terminal control system, which connects to a printer control system, which connects to a printer. This is really a bad question, but, If I had to pick straight away, I would go with D.