The sentence is about rioters who have destroyed the glass fronts of shops, such that they have been reduced to bits. From the given options, the words shattered and smashed both mean 'broken into pieces'. As the glass was broken to bits and pieces, both these options are correct. The word 'fled' means 'ran away from', which does not describe the action that resulted in the damaged glass fronts. Hence, option A is incorrect. Floating means 'suspended in water in a way that doesn't make one sink'. The speaker is not talking about water, and this action would not result in the glass breaking, hence option D is incorrect.