Fill in the blank with a suitable preposition.
Riya's Dad was walking _______ the riverbank.
The preposition ‘along’ is used when we talk about following a line of some kind, like a road, river or path. In the given context, Riya’s Dad is walking in line or parallel to the riverbank, thus ‘along’ is the apt answer. Hence option C is correct. The prepositions 'with', ‘below’ and ‘for’ are inappropriate in the given context. The preposition 'with' is used to denote company. The person is not accompanied by 'the riverbank', hence option A is incorrect. ‘Below’ means lower than something. One cannot walk ‘below’ the riverbank since it would be full of water. Thus option B is incorrect. 'For' is a preposition of reason that cannot be used here. Riya's Dad is not walking for the sake of the riverbank. Hence option D is incorrect.