Which of the following is responsible for the formation of an embryonic shoot called axillary bud?

Apical meristem is a completely undifferentiated meristematic tissue found in the buds and growing tips of roots in plants. Its main function is to begin growth of new cells in young seedlings at the tips of roots and shoots (forming buds, among other things). The axillary bud is an embryonic shoot which lies at the junction of the stem and petiole of a plant. As the apical meristem grows and forms leaves, it leaves behind a region of meristematic cells at the node between the stem and the leaf.