问题：

[单选] Which statement describes the rule of split horizon?（）

A . Only router can split boundaries(horizons)between concentric networks.
B . All distance vector protocols require fall routes that may cause momentary loops as the topology changes.
C . Networks can only remain fully converged if all information about routes is sent out all active interfaces.
D . Information about a route should not be sent back in the direction from which the original update came.
E . Each AS must keep routing tables converged to prevent dead routes from being advertised across the AS boundary.