What is Phantom RP used for?

A.
it is used for load balancing in bidirectional PIM

B.
it is used for redundancy in bidirectional PIM

C.
it is used for redundancy in PIM-SM

D.
it is used for load balancing in PIM-SM

Explanation:
Phantom RP
In Bidirectional PIM (Bidir-PIM), the RP does not have an actual protocol function. The RP acts as
a routing vector in which all the traffic converges. The RP can be configured as an address that is
not assigned to any particular device called a Phantom RP. This means that the RP address does
not need to reside on a physical router interface, but can just be an address in a subnet. The RP
can also be a physical router, but it is not necessary.

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6552/whitepaper_c11-508498.html