How Does Carbon Dioxide Enter a Leaf

How does carbon dioxide enter a leaf?

A) Atmospheric pressure forces CO₂ through pits on the leaf surface.
B) Dissolved CO₂ is transported from roots to leaves in the xylem.
C) CO₂ diffuses through the epidermis into the mesophyll.
D) CO₂ is moved by active transport into the leaf by special cells called guard cells.
E) CO₂ passes through openings called stomata on the leaf surface.