The correct option is B Agrobacterium tumefaciens
Ti plasmid or tumor inducing plasmid is isolated from Agrobacterium tumefaciens and is used as vector for transferring transgenes to plants. Gene of interest to be transferred is inserted into Ti plasmid by genetic engineering methods. This plasmid is then inserted into Agrobacterium tumefaciens . The plant cells are then exposed to Agrobacterium tumefaciens. The bacteria infects plant cells and plasmid integrates with plant genome thereby transferring the gene of interest to the plant genome.