The correct option is A Elongation of internodes
Gibberellin is a plant growth promoter. One of the functions of gibberellin is that it helps in the elongation of stem or internodes. Grape stalks and sugarcane crops are sprayed with gibberellins for the elongation of internodes. It can increase the length of the sugarcane stem thus increasing its yield as much as 20 tonnes per acre.
Curving of the protective sheath of an emerging shoot apex in an embryo called coleoptile is due to the higher concentration of auxin on the shady side. This causes the plant cells on that side to grow more so it bends toward the light.
Cytokinin is a plant growth promoter. They are found in the regions of rapid cell division e.g in root apices. It helps in cytokinesis (a division of the cytoplasm of a parent cell into 2 daughter cells), production of leaves, chloroplast in leaves, lateral shoot growth and adventitious shoot formation.
Auxin is a plant growth promoter that helps in root initiation. They are produced by the root apex and shoot apex. They initiate root formation in stem cuttings, promotes flowering and promotes natural detachment of old leaves and fruits termed as abscission.