Which Cisco NAC Appliance design is the most scalable in large Layer 2-to-distribution implementation?

A.
Layer 2 out-of-band

B.
Layer 2 in-band

C.
Layer 3 out-of-band

D.
Layer 3 in-band

Explanation:
https://www.safaribooksonline.com/library/view/foundation-learning-guide/9780132652933/ch08.html
“Layer 2 In-Band Designs The Layer 2 in-band topology is the most common deployment option.
[…]
This is the most scalable design in large L2-to-distribution environments, because this design can be transparently implemented in the existing network supporting
multiple access layer switches. It supports all network infrastructure equipment. The Cisco NAS supports per- user ACLs.”