Ahistorian compares transcripts of speeches delivered by powerful leaders throughout world history. these transcripts serve as which of the following?

Speeches of powerful leaders are primary sources: sources directly collected from the people involved, not compiled based on other sources.

Additionally, leaders often speak to motivate their people, so it's likely that it would serve as a good primary source for the general feelings and opinions of different sides of conflicts (compare Hitler's and Churchill's speeches)