Hey people! I have returned with another question! I need the answer of someone certified.
First, if you have a new question, please open a new post. Second, most of the people who help out on this site are not certified English teachers, but that doesn't really matter because they are very good at answering questions like yours.
Heaven and Hell do exist. Heaven and Hell do not exist. The cat and the dog enjoy taking a walk.
Each underlined phrase functions as a plural subject, so the verb should also be plural, do and enjoy. Here's a trick: try replacing the subject with a plural subject pronoun, they:
They do exist. They do not exist. They enjoy taking a walk.