Lateral shoot growth: Cytokinin is a plant hormone that plays a crucial role in promoting lateral shoot growth. It stimulates cell division and elongation, leading to the development of lateral shoots or branches. This hormone helps in the overall growth and branching of the plant.

Promoting leaf senescence: Contrary to the statement, cytokinin actually delays leaf senescence. Leaf senescence refers to the natural aging process of leaves, which involves the breakdown of chlorophyll and degradation of cellular components. Cytokinin inhibits the breakdown of chlorophyll and promotes the synthesis of proteins and enzymes that help delay leaf senescence. Therefore, it is incorrect to say that cytokinin promotes leaf senescence.

Adventitious shoot formation: Cytokinin also plays a significant role in promoting adventitious shoot formation. Adventitious shoots are shoots that arise from non-traditional locations, such as roots, callus tissues, or stems. Cytokinin stimulates cell division and differentiation, which leads to the formation of adventitious shoots. This property of cytokinin is utilized in various plant propagation techniques, such as tissue culture and micropropagation.

Overcoming apical dominance: Apical dominance is a phenomenon where the growth of lateral buds is inhibited by the presence of the apical bud or shoot tip. Cytokinin helps overcome apical dominance by promoting lateral bud growth. It stimulates cell division and elongation in the lateral buds, allowing them to develop into branches. This leads to a more bushy and branched plant structure.

Promoting leaf senescence: The correct answer is option 'B' because cytokinin does not promote leaf senescence. Instead, it delays leaf senescence by inhibiting the breakdown of chlorophyll and promoting the synthesis of proteins and enzymes that help maintain leaf function and prolong their lifespan.

In conclusion, cytokinin plays a crucial role in lateral shoot growth, adventitious shoot formation, and overcoming apical dominance. However, it does not promote leaf senescence; instead, it delays the aging process of leaves.