I was hoping that you could/would answer the following question:
Jason Mraz' 'I won't give up' is in the key of D. Still in the bridge he suddenly throws in a C and an A7/C#, how would you call that, change of key? Change of mode? And which ones? Mixolydian?
Then at the end, Jason plays this song obviously in lots of different ways, but in some recordings he ends it by throwing in a Bb, then C/Bb and finally D. So what mode is that? Or what is happening there? I've seen such a progression in several other songs and am just wondering what it is theoretically.
Hope you can shine some light on it, thanks!

Ness
(starting at 4.22)