GrammarNaziChallenge: Sentence 2

Here is the corrected sentence:

Which of the following sentences is grammatically correct?

1. The cat in the hat is very happy.
2. The cat is in the hat, is very happy.
3. The cat is in the hat, very happy.
4. The cat in the hat, is very happy.

Choose the correct one, and proceed to Level 5: Paragraph 2.