When A. tumefaciens is used to make a transgenic plant, a gene of interest is inserted into a _________, which is first transformed into __________. The __________ is then transferred to a plant.

a. viral vector, E. coli, gene of interest

b. T-DNA vector, A. tumefaciens, T DNA carrying the gene of interest

c. T-DNA vector, A. tumefaciens, gene of interest alone

d. T-DNA vector, E. coli, gene of interest alone