单项选择题
A．often used when communicating by touch B．necessary for satisfactory communication by gesture C．the only highly developed system of communication D．the most developed form of communication based on heating
A．They can be used to communicate over long distances. B．They require both a sender and a receiver. C．They involve use of conventional signs and symbols. D．They utilize the senses for reception.
A．Touch is not important as a means of communication. B．There is no well-developed system of communication based on touch. C．It is possible to communicate intelligently by touch alone. D．Touch must accompany visual communication.