Why does gladwell used the word “bargain”instead of agreement

In a series of experiments, hershey and chase radioactively labeled dna and protein in viruses and then used labeled viruses to infect bacteria. hershey and chase's experiments definitively showed that a. dna and not protein is the genetic material. b. dna and protein work together as a cell's genetic material. c. protein and not dna is the genetic material. d. neither dna nor protein act as a cell's genetic material