Which one of the following bacteria has found extensive use in genetic engineering work in plants?

Question

$\begin{array}{1 1} (a)\;\text{ Clostridium septicum} \\ (b)\;\text{ Xanthomonas citri} \\ (c)\;\text{ Bacillus coagulens} \\ (d)\;\text{ Agrobacterium tumefaciens } \end{array}$