What can be defined as a data structure that enumerates digital certificates that were issued to CAs but have
been invalidated by their issuer prior to when they were scheduled to expire?

A.
Certificate revocation list

B.
Certificate revocation tree

C.
Authority revocation list

D.
Untrusted certificate list

Explanation:
An Authority Revocation List (ARL) is a list of serial numbers for public key certificates issued to certificate
authorities that have been revoked, and therefore should not be relied upon.
Incorrect Answers:
A: A certificate revocation list (CRL) is a list of serial numbers for certificates that have been revoked, and
should therefore, no longer trust entities presenting them.
B: A certificate revocation tree is a mechanism for distributing notices of certificate revocations, but is not
supported in X.509.
D: A list of untrusted certificates is known as an untrusted CTL. It does not contain revoked certificates, but
untrusted ones.

https://en.wikipedia.org/wiki/Revocation_list
http://zvon.org/comp/r/ref-Security_Glossary.html#Terms~certificate_revocation_tree
https://technet.microsoft.com/en-us/library/dn265983.aspx