Answer:
c. To allow gas exchange between the environment and the inside of leaves.
Step-by-step explanation:
Stomata are small openings on the surface of the leaves of green plant that mediate the exchange of gases between the leaf and atmosphere.The stomatal aperture is Guarded by elongated bean shaped cells called guard cell. In grasses the guard cells are dumbell shaped. The turgidity and flaccidity of the guard cells control the opening and closing of stomata andthus regulate the exchange of gases during day and night.