Which of the following four CRS components must be active on a Historical Reporting Database (HRDB) and Call Recording expansion server?（）

A.It can be used in conjunction with another step. 
B.It allows the application programmer into another section of the application. 
C.Most of the Extended Get Digit String variables can be changed while the application is running. 
D.It allows the entry of a Boolean expression for the Interruptible and Clear DTMF Buffer on Retry fields.

A.The subflow cannot call additional or "nested" subflows. 
B.The subflow cannot transfer the contact to another resource. 
C.The subflow has full contact control and can perform any action that the parent flow can perform.

A.Erlang B 
B.Erlang C 
C.AHT * BHCA 
D.VG ports + CTI ports