A Researcher Proposes That the Relationship Between a Particular Bacterial

A researcher proposes that the relationship between a particular bacterial species that produces a fat-soluble vitamin is mutualistic with its insect host.Which of the following procedures would best test the researcher's hypothesis?

A) Determine which antibiotic kills the bacteria without harming the host,then administer this antibiotic to the insect and compare its growth with and without the vitamin
B) Determine which insecticide kills the insect without harming the bacterial host,then compare vitamin production by the bacteria from insects treated with the insecticide to those from untreated insects
C) Design a method to isolate the bacteria from the insect,then mutate the bacteria in the region of DNA that controls vitamin production and compare growth of the mutant and wild-type bacteria on minimal media
D) Extract the DNA from the bacteria and from the insect,then use reverse-transcriptase PCR and primers specific to the gene that controls vitamin synthesis to compare transcription of RNA in both organisms