简述陕甘宁边区宪法原则的主要内容。

函数f(x)=cos3x-sin2x是()

病人需求的医疗服务实体或外在质量是广义医疗服务的第二层次,即是

Passage 1

Today television is one of the most popular forms of entertainment in the home. Some people in places where television reception is good may think that television has taken the place of radio. Television, however, is actually a kind of radio. It uses special equipment for sending and receiving the picture. The television sound system uses the same type of equipment that is used in other forms of radio. Exchanging messages with ships at sea was one of the first uses of radio. Modern radio is still used for this purpose and for communication across oceans. On land too radio provides a means of instant communication even with moving vehicles such as taxicabs or service trucks. Police forces use two-way radio to get information to and from officers in squad cars and on motorcycles. Small portable sets make it possible to communicate with a central exchange while walking or riding in a city or over a countryside. Observers in airplanes can report traffic accidents and traffic jams by radio to police officers on the ground. Radiotelephones are used in many places. Connection with the regular telephone service can be provided for boats, trains, and cars. Isolated places in deserts, forests, and mountainous regions are linked by radiotelephone in many parts of the world. Thus by means of radio people can communicate with others wherever service is provided.

According to the passage, television ______.