The correct option is D Presence of bulliform apparatus.
Bulliform cells are large, bubble shaped epidermal cells that occur in groups on the upper surface of the leaves of many grasses. Loss of turgor pressure in these cells causes leaves to roll up during water stress. During drought, the loss of moisture through vacuoles induces bulliform cells to cause the leaves of many grass species to close as the two edges of the grass blade fold up toward each other.
Once adequate water is available, these cells enlarge and the leaves open again. So, leaves of grasses roll and unroll due to presence of bulliform apparatus and not because of hormonal change, change in temperature or change in pressure.
Thus, the correct answer is option D.