The meristematic tissues A, B and C depicted in the picture are:
Apical, intercalary, and lateral respectively.
Apical meristem is present at the growing tips of stems and roots and increases the length of the stem and the root. Tissues present around the edges in a lateral manner are called lateral meristem.The girth (width) of the stem or root increases due to lateral meristem (cambium). Intercalary meristem is present at the base of the leaves or internodes (between two nodes) on twigs.