The correct answers are: accuracy and honesty.
Indeed, being a historian take a lot of patience since research takes lots of effort and money. Accuracy in important, since the thread of events, the people involved and the multiplicity of factors that influence an event need to be carefully studied, verified and analyzed. Honesty is paramount, since past history inevitably has had an effect on present times and any falsification would not only have devastating effect in current politics but also would inevitably damage research on other fields which depend on history to yield accurate and satisfactory results. This is why bias is definitely to be banned from the profession.