Many farmers now grow insect-resistant varieties of cotton. the gene for the favorable trait, in this case, insect resistance, is transferred to the cotton's dna using. a) viral vectors. b) tissue culture. c) bacterial plasmids. d). in vitro fertilization.

Both viral vectors and bacterial plasmids can be used to transfer genes into an organism. An invitro fertilisation could maybe be helpful, but not with engineered genes, but existing genes.

A) viral vectors is the best answer is viruses can be used to infect plants and  change their DNA- bacteria aren't as good, as they can mostly be used to modify other bacteria only