T. Rex – Ballrooms Of Mars (Guitar Intro Tab)

Ive been trying to find a tab of this for ages, so i thought id have a stab at it.. This is main riff pattern that i think is just played over and over throughout the song. Its played quite loosely, i prefer to hit the bass notes of the chords then strum the higher notes slightly afterwards so thats why the chords appear slightly off-kilter. Havent got a clue what the A? actually is, sounds a bit diminished but not sure....anyway hope its ok!Enjoy!! RIFF 1

   C      B/C     A   A?
E-----8------------5--5
B-----8------------5--5
G-----9----9-------6--5  substitute the A? (dont know what chord that is)
D---10-----10-----7---6  with a standard barred D chord
A---10-----10-----7---6
E---8------7------5---5

C B/C A A? You gonna look fine, be primed for dancing C B/C A D You gonna trip and glide along the trembling plane REPEAT OVER FOR REST OF SONG I THINK

Substitute the A? with a standard barred D chord when you get to the end of the second line ie 
E-5
B-7
G-7
D-7
A-5
E--

This is my first tab but i think it sounds ok. Dont ask about the solo, i cant double track with an acoustic! Any suggestions, opinions send to [email protected]