No apostrophe when "its" is an adjective!

Simple, isn't it?

When "its" is an adjective, like "my" or "your" or his" or "their", you don't use an apostrophe.

You don't write "hi's door", you write "his door"; you don't write "it's door", you write "its door".

Which door? His door! Its door!

Just too easy!