问题：

[单选] What does qos pre-classify provides inregardto implementing QoS over GRE/IPSec VPN tunnels？（）

A .  enables IOS to copy the ToS field from the inner （original） IPheader to theouter tunnel IP header
B .  enables IOS to make a copy of the inner （original） IP header and to run a QoS classification before encryption， based on fields in the inner IP header.
C .  enables IOS to classify packets based on the ToS field in the inner （original） IP header
D .  enables IOS to classify packets based on the ToS field in the outer tunnel IP header
E .  enables the IOS classification engine to only see a single encrypted and tunneledflow to reduce classification complexity