Refer to the exhibit.

What does the incoming interface of the above (*, G) entry indicate?

A.
The interface closest to the source, according to the unicast routing table

B.
The interface where an IGMP join has been received

C.
The interface with the highest IP address

D.
The last interface to hear a PIM (*, G) join

E.
The interface closest to the RP, according to the unicast routing table

Explanation:

Source Trees
A source tree is the simplest form of distribution tree. The source host of the multicast traffic is
located at the root of the tree, and the receivers are located at the ends of the branches. Multicast
traffic travels from the source host down the tree toward the receivers. The forwarding decision on
which interface a multicast packet should be transmitted out is based on the multicast forwarding
table. This table consists of a series of multicast state entries that are cached in the router. State
entries for a source tree use the notation (S, G) pronounced S comma G. The letters represents
the IP address of the source, and G represents the group address.
Shared Trees
Shared trees differ from source trees in that the root of the tree is a common point somewhere in
the network.
This common point is referred to as the rendezvous point (RP). The RP is the point at which
receivers join to learn of active sources. Multicast sources must transmit their traffic to the RP.
When receivers join a multicast group on a shared tree, the root of the tree is always the RP, and
multicast traffic is transmitted from the RP down toward the receivers. Therefore, the RP acts as a
go-between for the sources and receivers. An RP can be the root for all multicast groups in the
network, or different ranges of multicast groups can be associated with different RPs.
Multicast forwarding entries for a shared tree use the notation (*, G), which is pronounced star
comma G. This is because all sources for a particular group share the same tree. (The multicast
groups go to the same RP.)
Therefore, the * or wildcard represents all sources.
Additional Information from Microsoft
Multicast traffic from source 162.10.4.1 (for example) uses the RPT, meaning the source sends it
to the RP rather than to the multicast group (the router would denote this by having a (*, G) entry
rather than a (S, G) entry). Before sending this traffic, Router 1 checks its unicast routing table to
see if packets from the RP are arriving on the correct interface. In this case they are, because they
arrive on interface I1, and the packets are forwarded.

http://technet.microsoft.com/en-us/library/bb742462.aspx