"No, it is not a monkey."
Translation:No, non è una scimmia.
i'm really terrible at Italian because it's been a few days i started the Italian , but i with all things i already know i think you use ""è"" when it's about everything expect human , and ""sei"" when it's about human , actually ""sei"" means (you are) i hope it help you :)
"Lo" is a direct object pronoun, not a subject pronoun. That means it can only receive the action, not do the action.