"to be" - answer rules
Are trees blue?
No. They aren't.
or
No. Its aren't.

Question

"to be" - answer rules
Are trees blue?
No. They aren't.
or 
No. Its aren't.

Answer

No. They aren't.

Answer

No. They aren't.

Answer

I am
we / you / they are
he / she/ it is

"it" is not plural so you can't use it for "treeS'

Answer

Are must also be responded by Are that describes plurality, thus

Q: What are these ?
A: These are trees.

However, since this question below is not about plurality, thus
Q: Are you James Bond ?
cannotbe responded using : Yes, I are James Bond
should be:
A: Yes I am James Bond (literally : I IS James Bond)