What Do Good Historical Studies Ensure

What do good historical studies ensure?

A) That what we see around us today is enough information to create theories that explain the past.
B) That in order to fully understand our history we need to guess.
C) That the information uncovered is not the only history or truth. There are lots of truths existing at every point in time.
D) That we must think of ourselves now, what has happened in the past is not useful as we make progress.