I think it's quite difficult to make a fire with only a drink can and a bar of chocolate. Perhaps cutting the can from the top to the bottom, oppening it and polishing the inner part of the can so that you have an area to catch the sunbeams. Then you will have to put the paper of the bar of chocolate on a little area of the polished can so that it can be fired by the hot of the can in the sunlight.
Well, after looking for some information about how to make a fire with a bar of chocolate and a drink can, I found the answer to the quiz. It's better than mine (I suppose the method I explained before doesn't work almost never) but it's not very far from my idea.