The correct option is A both a and b
Apical meristems are found in the root and shoot apex and are responsible for the increase in the length of the plant axis.
The intercalary meristems are formed from the apical meristems as the latter continues to divide. The intercalary meristems help in increasing the length of the plant and is most commonly seen in monocots.
If the cells of the meristem originated from cells that had differentiated and again resumed meristematic activity, the meristem is known as secondary meristem. It is responsible for the secondary growth of the plants which includes the increase in the girth of the plant axis.