If Organization A trusts Organization B and Organization B trusts Organization C, then Organization A trusts Organization C. Which of the following PKI concepts is
this describing?

A.
Transitive trust

B.
Public key trust

C.
Certificate authority trust

D.
Domain level trust

Explanation:
In transitive trusts, trust between a first party and a third party flows through a second party that is trusted by both the first party and the third party.
Incorrect Answers:
B: Public keys are part of Public Key Infrastructure (PKI) and are used together with private keys in an asymmetrical cryptography system.
C: A Certificate Authority (CA) is responsible for issuing, managing and maintaining certificates in a Public Key Infrastructure (PKI). The certificates are used as a
means of authentication. This, however, is not a trust model.
D: Domains exist within a single organization and represent the trust of entities within the domain. This trust is not extended to third parties.

Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, Sixth Edition, Sybex, Indianapolis, 2014, pp 251- 252, 332-333
https://technet.microsoft.com/en-us/library/cc731335.aspx