The correct answer is A. Apical meristem
Step-by-step explanation:
In plants, the primary growth refers to the type of growth that increases the length of the stem or toots in opposition to the secondary growth in which the stem thickens and that occurs as the result of the vascular cambium. However, in the case of primary growth, this can be explained mainly due to the action of apical meristem that is a type of tissue located in the tips of roots and the stem and therefore the type of tissue in which the growth takes place mainly through cell division. Considering this, it can be concluded primary growth is due to the action of the apical meristem.