I'm not sure, but I think a friend of mine did that voice-over for chocolates. (MIGHT) That voice-over for chocolates _____ a friend of mine.

I'm almost positive Susan heard what I said. (HAVE) Susan _____ heard what I said.

It was a mistake for me to buy this computer game. (BOUGHT) I _____ this computer game.

I'm sure Rafael Nadal earned a lot for that car advert. (BEEN) Rafael Nadal _____ a lot for that car advert.

John looks much fitter. I think he's stopped smoking. (GIVEN) John must _____ smoking. He looks much fitter.

May be Tom didn't want to come. (NOT) Tom _____ to come.