What does this wait event indicate?

You look at the Top 5 Timed Events section of the Automatic Workload Repository (AWR) report
and find that the wait event buffer busy waits is consuming a significant portion of DB time. What
does this wait event indicate?

A.
buffer cache too small

B.
insufficient DBWn processes

C.
excessive block replacement

D.
a large number of locally-managed tablespaces in the database

E.
block contention on segment headers, data blocks, undo header, or undo blocks