Which plant hormone promotes cell growth and prevents fruit drop?

The correct answer is auxins, which are important plant hormones that play a significant role in promoting cell elongation and growth. Auxins are primarily produced in the apical meristem of plants and they help stimulate the growth of stems and roots. In terms of fruit development, auxins are responsible for inhibiting the dropping of fruits before they are fully mature. By promoting cell division and growth within the fruit and connecting tissues, auxins help ensure that fruits are retained on the plant until they are ready for dispersal.

The roles of other hormones in the list differ from those of auxins. Cytokinins, for instance, promote cell division and can delay aging in leaves, but they do not specifically prevent fruit drop. Ethylene, on the other hand, is associated with fruit ripening and can promote the dropping of fruit once it is ripe. Abscisic acid functions primarily as a stress hormone, aiding in responses to environmental stresses, and it can promote fruit drop, which is contrary to the role of auxins. Thus, auxins are uniquely positioned to both promote growth and prevent premature fruit drop in plants.