Final answer:
Newly-formed root cells begin to form different cell types in the meristem.
Step-by-step explanation:
The newly-formed root cells begin to form different cell types in the meristem (option c).
Apical meristems are responsible for the primary growth of plants and differentiate into three types of meristem tissues: protoderm (epidermis), ground meristem (ground tissue), and procambium (xylem and phloem).
These three types of meristem tissues allow the growth in length or height of plants and give rise to different cell types in the root.