Television first (17) ______ some fifty years ago in the 1950s. Since then, it (18) ______ one of the most (19) ______ sources of entertainment for both the old and the young. Television offers cartoons for children, world news, music and many other (20) ______. If someone is interested in sports, for (21) ______, he can just choose the right sports channel. There he can enjoy a broadcast of an international football match (22) ______ it is actually happening. Television is also a very useful way for companies to advertise their products. It is not too hard for us (23) ______ why there is a TV set in almost every home today. And, engineers are developing interactive TV (24) ______ allows communication between viewers and producers.