The correct option is A Agrobacterium tumefaciens
Agrobacterium tumefaciens will transfer genes (T-DNA region of Ti plasmid) into the plant that produces its food or nutrient called opines (opines are not needed for plants). Apart from that, it also integrates genes for cell division and proliferation leading to crown gall disease, so that more number of cells result in more production of opines. Because of this reason it is called as a 'natural genetic engineer'.