The correct option is A of, in
The prepositions ‘of’ and ‘for’ are confused quite often. ‘Of’ is used to denote a material something is made of, the connection or belonging; while ‘for’ is used to indicate a reason, cause or purpose of an action. In the given sentence the piece that the crow has is made of cheese, hence preposition ‘of’ is suitable. Thus option B is incorrect. On the other hand prepositions ‘in’ and ‘at’ are both used to denote a place or position. But ‘in’ is used to talk about a place or position that is within a larger area or space, whereas ‘at’ is used to denote a point rather than an area. In the given sentence, the crow carries the piece of cheese ‘in’ its beak, because the piece would be held within the beak's hollow. The beak is not a point ‘at’ which a piece can be carried. Similarly, ‘with’ is not suitable since here it would mean that the piece of cheese is alongside the beak, and not held inside it. Therefore option A is correct, while C and D are incorrect.