[单选题]
The photomicrograph below shows a root tip meristem. Which p5 x1e9o.myyxof the following tt,vx i x2sh)x-l a:saw 5c5l-sentenxx,v-awx5 h:lt -)aissct 5l 2ces correctly 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
