What about Las casa's account is believable? why might he have exaggerated?

Explanation:

Las Casas was one of the few sources that reported directly on the atrocities that Spanish colonialism was inflicting (though it is far from the only source). ... Still, Las Casas is a verifiably reliable source regarding the reality of the treatment of natives under Spanish rule.

2686-2181 bce-- "egyptian civilization developed along the nile river in large part because the river’s annual flooding ensured reliable, rich soil for growing crops."

1069-664 bce-- "ancient egyptians developed wide-reaching trade networks along the nile, in the red sea, and in the near east."

the real answer is b