求高手解答几道通信英语选择题17. woth the introduction of digital data syst

求高手解答几道通信英语选择题
17. woth the introduction of digital data system, some subsribers that have been incorporated into the network.
A. can provide video service
B. transmit broadband program
C. contain a transmitter and receiver
一The celluar concept is defined by two feature
1.base station and mobile station
2. frequency reuse and cell splitting
3. sampling and coding
4.voice channel and data channel
27. These two forms of information, the speech and the data information, are the useful part of the transmission, but have to be supported .
A. by overhead information
B. by standards
C. by cell splitting
D. by many other types of information