Why were delaware, maryland, kentucky, and missouri considered border states during the civil war?
a. because they had boundaries on the ocean
b. because they were slave states that didn't secede
c. because they were free states that seceded
d. because they were free states next to slave states

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:

china is shifting toward specialization in industry and services and away from agriculture.

explanation:

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