When television first began to expand, very few of the people who had become famous as __31__ announcers were able to be equally effective __32__ television. Some of the difficulties they experienced when they were trying to __33__ themselves to the new medium were technical. When __34__ on radio, for example, they had become __35__ to seeing on behalf of the listener. This art of seeing for others __36__ that the announcer has to be very good __37__ talking. Above all, he has to be able to __38__ a continuous sequence (序列) of visual (视觉的) images which add meaning __39__ the round the listener hears. In the __40__ of television, however, the announcer sees __41__ with the viewer. His duty, __42__, is completely different. He is there to make __43__ that the viewer does not __44__ any point of interest, to help him focus __45__ particular things, to help him __46__ the images on the television screen. __47__ his radio colleague, he must know the __48__ of silence how to use it at those __49__ when the pictures speak for __50__.

A. television  B. advertisement  C. radio  D. newspaper