The correct answer is A. Stomata.
Stomata are tiny pores found on the underside of leaves. They allow for gas exchange between the plant and the atmosphere. Carbon dioxide enters the plant through the stomata, and oxygen and water vapor are released. Stomata are also responsible for transpiration, which is the loss of water vapor from the plant.
Lenticels are small, raised areas on the surface of stems and branches. They allow for gas exchange between the plant and the atmosphere, but they do not play a role in transpiration.
Hydathodes are small pores on the underside of leaves that release water droplets. They are most common in plants that grow in dry environments, and they help to prevent the plant from losing too much water.
Perforations are large holes in the walls of xylem vessels. They allow for the rapid transport of water and minerals from the roots to the leaves.
Here is a diagram of a leaf that shows the location of the stomata:
The stomata are located on the underside of the leaf, in between the cells of the epidermis. They are surrounded by a guard cell, which controls the opening and closing of the stoma. The stoma is a small opening that allows for gas exchange between the plant and the atmosphere.