As to actual key(I posted C because it is easiest to understand and transpose)--Martha and the Vandellas did it in E(E9th chord), as did The Mamas and the Papas, David Bowie and Mick Jagger's duet is in B, of all things, while Rockapella is in Bb--Greatful Dead in A--Van Halen in D--the Sister Act version was in Eb--Sorry, probably more than you wanted to know--