单项选择题
Which timing mode is appropriate for a SONET NE that is adjacent to a SONET NE using BITS-1 timing source?（）
A.DUS B.line timing C.loop timing D.internal timing E.through timing
单项选择题 If node 2 is accepting line timing from node 1, node 2 will send （）to node 1 as its SSM message.
单项选择题 SONET Code Violations (CVs) totals in the PM tables are actually an accumulation of the number of （）.
单项选择题 Scrambling of SONET signals is done to （）.
