_____ her eyes brown? Yes, they are!
Are
When is Christmas?
It´s on December twenty-fifth
Is Halloween on March?
No, it isn´t!
Is _____ hair brown? No, it isn´t! // (his/her)
her
when is your birthday?
...
Are his eyes blue?
Yes, THEY are
Is mother´s day on May?
Yes, it is!