The correct option is 2 and 3 only, as both cytoplasmic male sterility (CMS) and gene silencing are advanced biotechnological techniques utilized in the development of transgenic crops. CMS is often employed in hybrid seed production, enabling the expression of desirable traits without pollen fertility, thus facilitating the creation of hybrids with enhanced characteristics. Gene silencing, on the other hand, involves techniques such as RNA interference (RNAi) to suppress unwanted gene expression, allowing the development of crops with improved resistance to pests and diseases or enhanced nutritional profiles. Conversely, budding and grafting are traditional horticultural practices used for propagation and do not involve genetic modification, making them inapplicable in the context of transgenic crop development.