Asap! i don't understand this can anyone me? (it may or may not be the right subject ik, but plz me)

Layer B would 'be'(get it??) would be the oldest of the two because it came before layer D. The second part to the question I don't understand.

Its decreasing because of illnesses

The investiture controversy began as a power struggle between pope gregory vii (1072–85) and henry iv, holy roman emperor (1056–1106).[2] a brief but significant struggle over investiture also occurred between henry i of england and pope paschal ii in the years 1103 to 1107, and the issue played a minor role in the struggles between church and state in france, as well.by undercutting the imperial power established by the salian emperors, the controversy led to nearly 50 years of civil war in germany, and the triumph of the great dukes and abbots. imperial power was finally re-established under the hohenstaufen dynasty. historian norman cantor: