[单选题]
The photomicrograph below shows a root ti-u*y:eks :jpc l2 3wqyp meristi wfb*)vh4r.w 9mxw y9em. Which of the following sentences correctly defines a merisfbw y wm9w94x vhri.*)tem?
A. A region of a plant with differentiated cells that undergo cell division
B. A region of a plant with undifferentiated cells that undergo cell division
C. A region of a flower that undergoes cell division
D. A region of a plant where cell differentiation occurs in response to a change in day length
