A、Music. B、Railway stations. C、Talk shows. D、Radio stations. D综合各段主题，只有选项D能最好地概括主题。

Recorded music is the chief kind of radio entertainment. Most stations specialize in one kind of music, such as rock, classical, country and western, or "old-time favorites". Some stations broadcast several kinds of music.
    Radio stations that broadcast music have hosts who introduce and comment on the music. They play an important role. Each station tries to hire hosts whose announcing styles and personalities appeal to the station’s largest audience.
    Programs that provide information include newscasts, talk shows, and descriptions of sports events. Newscasts come on the air at regular times -- every half-hour or hour on most stations. In addition, radio stations present on-the-spot news coverage of such special events as political conventions, space flights, Senate hearings, and speeches by the President. Radio stations also broadcast such specialized news as weather forecasts, traffic reports, and stock market and agricultural information. Other news features include public service announcements about community events, activities of community groups, and. government services. A few stations broadcast only news to serve listeners who prefer news programs to music.
    Talk shows present discussions on a variety of topics and interviews with people from many professions. Each show has a host or hostess who leads the discussion or does the interviewing. The subject of a program may be a current political topic, such as an election of a government policy, or it may deal with a social issue, such as crime, pollution, poverty, racism, or sexism. Many talk shows allow listeners to take part in the program. Listeners are invited to telephone the station to ask questions or give their opinions about the topic.