What is the best example of a primary source document useful in the study of history?

Where did benjamin franklin travel to to seek aid for the colonists during the revolutionary war

Why was galileo galilei brought before the inquisition? for insisting that earth stands still at the center of the universe for proving that planets move in elliptical orbits for putting forth evidence that earth moves around the sun for suggesting that the sun is a star

Why did poland, hungary, and east germany join the warsaw pact? a)their people voted to join in free elections. b)their efforts to join nato failed. c)they wanted to stop the spread of communism in europe. d)they were soviet satellites that had little choice.