Final answer:
A T1 line contains 24 telephone channels, making option B the correct answer.
Step-by-step explanation:
The T1 line is a type of digital transmission service commonly used in North America that can carry voice and data communications. A T1 line consists of 24 telephone channels, each capable of transmitting voice or data at a rate of 64 kilobits per second (kbps). The correct answer to the number of telephone channels in a T1 line is B. 24.