It would be "(D) the bombing of the Oklahoma City Federal Building," that is not associated with Al Qaeda, since this was an act of "domestic terrorism," that was carried out by a Christian white male.
Brown v. Board of Education was a landmark case in which it was finally proven that segregation in institutions of education was highly unconstitutional, so you could say that that is the greatest effect since it made other schools become open for everyone as well.
An Incan citade in the Andes mountains in Peru. (Above the Urubamba River Valley) The original use of it is not known, but we do know it was built in the 15th century.
