Which of the following description of the AU pointer are correct? (Multiple choice)
A . The root cause of the AU pointer adjustment is that the clocks between the upstream and downstream stations are not synchronized.
B . Since the value of the AU-PTR pointer is placed in the last 10 bits of the two bytes H1 and H2, the valid value is 0~1023.
C . AU-PTR refers to the location of the J0 byte.
D . If the receiving end detects that the H1H2 byte is all "1", the local end generates an AU-AIS alarm.
Answer: AD