D."While facts can be proven, historical fiction includes imagined details to add dramatic interest." is your answer. This is because FACT is something that happened and is/can be proven true. FICTION is something which may have bases in the real world, but in reality can't be confirmed. Example:
Historical FACT: "When John Adams had been elected president, the white house wasn't even finished being built."
Historical FICTION: "John Adams looked up at the weary scaffolding of his soon-to-be home, and sighed."
The obvious difference here is that one IS what we know, vs. one being BASED on what we know. While we know the white house wasn't built at that time, we don't know for sure if John Adams looked up at it and sighed.