Using Enhanced Availability, how often does the database on the standby CUA get updated?

Using Enhanced Availability, how often does the database on the standby CUA get updated?

A.
Active CUA sends all database updates immediately to the Standby CUA

B.
Every 5 minutes or 500 writes, whichever occurs first

C.
User must define the frequency depending on the desired RPO

D.
Whenever the active CUA writes a backup of its database to Centera