Let me start off by saying i have been struggling with learning music theory but yet I am still trying. That being said I have just come up with a bassline that I am really digging. Now I would like to be able to expand off of it with guitar and all that but would like to figure out what key it is in and have been struggling. I know that the way it stands right now it should be able to be interpreted in different ways but I am not sure how. I am playing D G C D with passing tones of E and A. My first assumption would be it is a in the key of D something but I struggle with my modes. I would think D dorian would be ok to work out of but I am not sure of other options or even if thats the best option.