[单选题]
The photomicrograph below sdk;r+ yg7db,+ b;jwj dhows a root tip meriz7d zpu*j. ht5stem. Which of the following sentences cordupz 7.*5zjhtrectly defines a meristem?
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
