Scrambling of SONET signals is done to （）.

• A、prevent the leakage of external fiber emissions
• B、provide the optical network with the highest level of security possible
• C、assure an even distribution of 1's and 0's for extended transmitter life
• D、assure an adequate number of transitions for clock recovery at the receiver
• E、prevent the receiver from assuming AIS inadvertently when all 0's are received