Why was the middle ages period once reffered to
as the dark ages ?

We dont know much about this time.

Explanation:

Compared with other eras, historians dont know as much about this time. In some ways, this period of time has been lost to history

Because compared to other ages, historians didnt knowmuch about this time ,so it was kind of lost in time.

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:

what the first or next guy says