How does a certificate authority impact security?

How does a certificate authority impact security?
A . It validates client identity when communicating with the server.
B . It authenticates client identity when requesting an SSL certificate.
C . It authenticates domain identity when requesting an SSL certificate.
D . It validates the domain identity of the SSL certificate.

Answer: D

Explanation:

A certificate authority is a computer or entity that creates and issues digital certificates. CA do not "authenticate" it validates. "D" is wrong because The digital certificate validate a user. CA –> DC –> user, server or whatever.

Reference: https://en.wikipedia.org/wiki/Certificate_authority