Why does a modern transit AS not need to have BGP synchronization enabled?

A.
A modern transit AS does not rely on redistribution of BGP routes into an IGP.

B.
A modern transit AS does not rely on redistribution of IGP routes into an IGP.

C.
A modern transit AS rely on redistribution of BGP routes into an IGP.

D.
A modern transit AS rely on redistribution of IGP routes into an IGP.

E.
A modern transit AS uses peer group to reduce the BGP configuration complexity.

F.
Modern transit AS internal (core) routers do not run BGP. Internal (core) routers normally use a default route to reach all external networks.

Explanation:

Synchronization was used in older transit autonomous system design that relied on BGP route redistribution into IGP. Modern autonomous system designs cannot rely on this any more as the number of routes carried in the Internet eceeds the scalability range of any known IGP. Redistribution into IGP is thus no longer applicable and the synchronization feature has to be disabled in order for you transit autonomous system to work. Reference: Configuring BGP on Cisco Routers p.4-45