Who or What Was "Deep Throat

Who or what was "Deep Throat"?

A) The FBI code name for an investigation of corrupt newspaper editors in the 1970s
B) An adult film of the 1970s that was used as a test case for protection of pornography as free speech under the First Amendment
C) An Al Qaeda operative who was exposed after an undercover investigation by a major media alliance
D) A confidential informant who gave information to Washington Post reporters and eventually helped break the Watergate investigation in the 1970s
E) An investigation that delved deeply into the corrupt side of the media and its control by the government