The solution is A, but I think both A and C are correct. For choice C, stomata that protected by hairs will have a greater amount of water vapour around them, hence lower water potential gradient. Hence, this results in the reduction in the rate of transpiration, as well as choice A.
Though I don't come across graphs like these too often, I guess the answer should be A because...
From the graph, it is clear that Leaf 1 has more mass than Leaf 2 after 5 hours. This means there is a lower rate of transpiration in Leaf 1, which can definitely be explained by a thicker cuticle (since the thicker the cuticle, less is the water lost). Hence choice A is correct.
Now, look at choice C. Like you said, in leaves where stomata are protected by hairs, there will be lower rate of transpiration. Then, obviously Leaf 2 should have a higher mass than Leaf 1, right? But this is not the case (as per the graph). Hence, choice C is incorrect.