Explanation/Reference:
C: A callback handler used to control the failover and failback within a multi data source must include an implementation of the weblogic.jdbc.extensions.ConnectionPoolFailoverCallback interface.
D: You can register a callback handler with WebLogic Server that controls when a multi data source with the Failover algorithm fails over connection requests from one JDBC data source in the multi data source to the next data source in the list.
Incorrect Answers:
B: Frequency of these tests is controlled by the Test Frequency Seconds attribute of the multi source. The default value for Test Frequency is 120 seconds, so if you do not specifically set a value for the option, the multi data source will test disabled data sources every 120 seconds.
Reference: http://docs.oracle.com/cd/E23943_01/web.1111/e13737/
jdbc_multidatasources.htm#JDBCA223