I'm having trouble finding the answers to these fill-in-the-blank questions: Our understanding of the solar system has changed from an Earth-centered model of ____ and ____ to the sun centered model of _____ and _____.

Question

I'm having trouble finding the answers to these fill-in-the-blank questions: Our understanding of the solar system has changed from an Earth-centered model of ____ and ____ to the sun centered model of _____ and _____. 
I was thinking for the first 2 blanks: rocks; oxygen and for the last 2 blanks: gas;helium. If it isn't correct can you please give me a hint? Thank You!

Anonymous · Answer

Please help! I'm really having trouble with this!