Where does _________ come from?

Fill in the blank and you've got the question that Kira seems to ask about a million times a day. This morning in the car she asked where gas came from. I wanted to say something smart like, from your bottom, but I knew she really wanted to know, or at least she wanted to fill the dead air with her voice.
Ahh, so begins the conversation today in the car.....
Mommy, where does gas come from?
It comes from oil in the ground.
Why is there oily (and that's not a typo) in the ground?
Because it's a natural resource, god put it there.
Well (long and drawn out) why did he do that?
So we can have gas.
Where do pencils come from?
From wood.
Where does wood come from?
From the trees. Trees give us paper and wood.
But Mommy, (very matter of factly) trees are not yellow.
I had to start laughing here, because she was referring to the yellow pencils. Then I had to explain the paint.
There were many more questions, but I was trying to concentrate on finding the cabinet store so unfortunately I tuned her out the rest of the time. I do try to answer her as much as possible, but sometimes it's hard to tell how far I should really take it.

She is really into knowing where things come from. As of right now she thinks that babies come from mommy's tummy and people go to heaven when they die. As far as I am concerned that's fine by me forever.