What are two possible reasons for these wait events?

You are managing a policy-managed three-instance RAC database. You ran database ADDM for
the database and noticed gc current block congested and gc cr block congested waits. What are
two possible reasons for these wait events?

A.
The wait events indicate a delay in processing has occurred in the Global Cache Services
(GCS), which is usually caused by high load.

B.
The wait times indicate that the blocks must wait after initiating a gc block request, for the round
trip from the start of the wait until the blocks arrive.

C.
The wait events indicate that there is block contention resulting in multiple requests for access
to local blocks.

D.
The wait events indicate that the local instance making the request for current or consistent
read blocks was waiting for logical I/O from its own buffer cache at the same time.

Explanation:
Load-Related Wait Events
The main wait events for load-related waits are:
The load-related wait events indicate that a delay in processing has occurred in the GCS, which is
usually caused by high load, CPU saturation and would have to be solved by additional CPUs,
load-balancing, off loading processing to different times or a new cluster node. For the events
mentioned, the wait time encompasses the entire round trip from the time a session starts to wait
after initiating a block request until the block arrives
Oracle Real Application Clusters Administration and Deployment Guide