指出划线部分的语法现象。(1)The voice signal picked up by the microphone is digitized first and then compressed.(2)In GSM system, frequency-division multiplexing is used, with each mobile station transmitting on one frequency and receiving on a higher frequency.(3)The bandwidth available for compressed speech is just under 8kbps.(4)Each data frame contains two information fields, each one having a control bit.(5)The mobile station assigned to time slot 2 wants to transmit to the base station.