The kingdoms of ghana, mali, and songhai were all able to achieve golden ages in part because of their
(1)reliance on sugar plantations in the niger delta
(2)control of trans-saharan trade routes
(3)discovery of oil reserves in the gulf of guinea
(4)ability to use the natural harbors on the atlantic ocean coast

option d is correct. corroborated sources of historical evidence   is necessary to validate a claim about an event in history.

historians tend to use written sources, but audio and visual materials as well as artifacts are important objects that supply information to modern historians.

historical sources are usually divided into two categories: primary and secondary sources. depending on the historian's intent, some sources shift their designation. determining what type of sources toimplement, and the level of credibility and reliability of those sources, is a significant step in critical thinking for the historian.

explanation: