Persons who cannot see, hear, or speak are able to communicate through a system of ________.

A．communication actually takes place when the message is received
B．there are more means of receiving than of sending communications
C．reception of communications involves use of the senses
D．it is difficult to organize by the means of sending communications

A．often used when communicating by touch
B．the most developed form of communication based on hearing
C．the only highly developed system of communication
D．necessary for satisfactory communication by gesture