Comparisons were drawn between the development of television in the 20th century and the diffusion of printing in the 15th and 16th centuries. Yet much has happened【21】. As was discussed before , it was not【22】the 19th century that the newspaper became the dominant pre-electronic【23】, following in the wake of the pamphlet and the book and in the【24】of the periodical. It was during the same time that the communications revolution【25】up, beginning with transport, the railways and leading【26】through the telegraph, the telephone, radio and motion pictures【27】the 20th century world of the motor car and the airplane. Not everyone sees that process in【28】. It is important to do so.
It is generally recognized, 【29】, that the introduction of the computer in the early 20th century, 【30】by the invention of the integrated circuit during the 1960s, radically changed the process, 【31】its impact on the media was not immediately【32】. As time went by, computers became smaller and more powerful, and they became personal too, as well as【33】, with display becoming sharper and storage【34】increasing. They were thought of, like people,【35】generations, with the distance between generations much【36】.
It was within the computer age that the term information society began to be widely used to describe the【37】within which we now live. The communications revolution has【38】both work and leisure and how we think and feel both about place and time, but there have been【39】views about its economic, political, social and cultural implications. Benefits have been weighed【40】harmful outcomes. And generalizations have proved difficult.
(21)

A. between
B. before
C. since
D. later