If All Cells of a Plant Have Identical DNA, Then

If all cells of a plant have identical DNA, then why are there different cell types and tissues within a plant?

A) Different subsets of the information are used in each type of cell.
B) Internal environmental conditions may determine which subset of the genome is expressed.
C) Hormones and other growth regulators may control gene expression.
D) External environmental conditions such as light or dark may alter gene expression.
E) All of the above may influence the expression of different subsets of genetic information from the genome, resulting in differentiation and development.