Note that this question is a strengthen question. We need an answer choice that supports the argument that Caligula may not have been as cruel or insane as we thought he was. (A) is wrong because even if there's less documentation for Caligula's reign than others, there's no reason to not trust the little documentation that we have now. We need evidence that suggests this documentation is wrong, and that's what (C) provides us. The histories, which were written by Caligula's enemies, may have just been composed of stereotypical evil tyrant acts that Caligula's enemies attributed to him. Hope this helps!