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

A.
BGP requires redundant TCP sessions between iBGP peers.

B.
A full mesh allows for optimal routing within the Transit AS.

C.
Routes learned via iBGP are never propagated to other eBGP peers.

D.
Routes learned via iBGP are never propagated to other iBGP peers.

E.
Routes learned via eBGP are never propagated to other iBGP peers.