Which of the following statements about the multiplex section remote error indication (MS-REI) is correct?
① The B2 byte indicates the transmission channel.
② The M1 byte indicates the transmission channel.
③ MS-REI is transmitted from the sink to the source.
④ MS-REI is transmitted from the source to the sink.
⑤ Indicates the number of detected bit errors after the sink receives the MS signals.
A . ①④⑤
B . ②④⑤
C . ①③⑤
D . ②③⑤
Answer: D