PLEASE HELP ASAP!!!

Water vapor is leaving a leaf through open stomata. Why are the stomata pores open?

A. The pores open during the day when the plant receives light energy.
B. The pores are held open by guard cells that are full of water and stiff.
C. The pores are pushed open by the water vapor leaving the leaf
D. The pores open when the guard cells are empty and limp.