Brain freeze, how would you write this?

With a series of questions in a sentence like if you were written down a list to ask someone. Would you separate each one with a ',' like you normally would with a series of random stuff or end each one with a question mark?

For example: Why is the sky blue, why is the grass green, and what is your favorit color?

or

Why is the sky blue? why is the grass green? what is your favorit color?

thx

the second example is right ! you don't put commas after question just...
example:
Sara, Tim, brad, and I went to the movies. would be commas but I might be wrong !!!

You got me on that one! I have no idea! Why didn't I think about that? Oh, probably because I am a bad speller!