What are the advantages of IPSec-based site-to-site VPNs over traditional WAN networks?

What are the advantages of IPSec-based site-to-site VPNs over traditional WAN networks?

A.
Delay guarantees, span, performance, security and low cost

B.
Span, flexibility, security and low cost

C.
Bandwidth guarantees, support for non-IP protocols, scalability and modular design guidelines

D.
Bandwidth guarantees, flexibility, security and low cost