Computers have become a familiar medium of communication, connecting people around the world. Answer: c. medium
This question is fishing for "medium" as the answer, but I have a big problem with that. Computers are not the medium of communication. The internet is, or fiberoptic and microwave and telephone lines are. The computer is the device that you use to access the medium, and interface yourself with it. There were computers around for 30 years before anybody had access to an internet. During that time, you could sit in front of a computer all day and work on your own programs and "apps", but if you wanted to communicate with anybody else, you still had to call him on the phone, write him a letter, or take a deck of punched Hollerith cards over to where he was. The computer itself is not a medium of communication. So there !