Proponents of popular sovereignty believed that:
a. all slaves should be declared free
b. southerners were too unreasonable for a fair debate on slavery
c. residents of a territory should decide the issue of slavery
d. presidential elections should not be decided by the electoral college

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:

according to my research (britannica and quizlet) the first settlements were along the huang river because it could give the crops more fertile soil that really it out. this was due to the yellow slit caused by floods of the river.