Which of the following reasons will cause HDFS NameNode to enter safemode (safe read-only mode)? (multiple choice)

Which of the following reasons will cause HDFS NameNode to enter safemode (safe read-only mode)? (multiple choice)
A . The disk space where the metadata of the active and standby NameNodes reside is insufficient.
B . The number of lost blocks exceeds the threshold.
C . The missing copy exceeds the threshold.
D . The damaged copy exceeds the threshold.

Answer: AB