What Is a Digital Certificate

What is a digital certificate?

A) It's a means of establishing the validity of an offer from a person,entity,web site or e-mail.
B) It's a centralized directory wherein registered keys are created and stored.
C) It's a means of establishing your credentials electronically when doing business or other transactions on the Web
D) It's an entity that generates electronic credentials and distributes them upon proving their identity sufficiently.