1 use
2 People can watch TV and listen to it,but they can’t take part in what they see.翻译：电视有画面和声音,但人们没办法参加他们看到的.
3 Radio,telephone and television （are widely used in the world）
4 相似句 Vision-phones can be of great use when you have something to show the person whom you are calling.
5 主题句With the vision-phone,two persons who are talking can see each other.