What causes the stoma to open?
OA. When the guard cells inflate with oxygen, they become stiff and
the pore opens.
B. When the guard cells are empty, they become limp and the pore
opens.
OC. When the guard cells get covered in wax, they become limp and
the pore opens.
D. When the guard cells are full of water, they become stiff and hold
the pore open.