The correct option is A It can kill harmful bacteria.
Bacillus thuringiensis is a bacterium that produces a toxin, which when ingested by cotton bollworm brings about their death. Hence, it can be used as an environment-friendly pesticide or insecticide. However, it has no action on bacteria or fungi which are harmful to plants. It's spores can be sprayed on crop plants. Bt-Cotton has been genetically engineered for containing the gene coding for the toxin of Bacillus thuringiensis.