Why should iBGP sessions be fully meshed within a Transit AS ?

[PlAwAnSaI]

All of the IBGP routers in the network have peer relationships built with every other
IBGP router in the network. Why should iBGP sessions be fully meshed within a
Transit AS?
A. Routes learned via EBGP are never propagated to other IBGP peers.
B. Routes learned via IBGP are never propagated to other IBGP peers.
C. A full mesh allows for optimal routing within the Transit AS.
D. Routes learned via IBGP are never propagated to other EBGP peers.
E. BGP requires redundant TCP sessions between IBGP peers.
F. None of the other alternatives apply.