The effects of the treatment remain, regardless of how long it takes to administer. We are concerned with the end result and need an explanation for why treated chicks have lower Salmonella rates but higher levels of the other bacteria after the treatment is administered.

We are not concerned with the initial rates of Salmonella in young chicks. Instead, we are looking at the change in the rate of Salmonella and the other variety of bacteria after chicks receive treatment.

Adult chickens' resistance to bacteria doesn’t tell us about bacteria levels in young chicks. Also, even if the chicks are resistant to many harmful bacteria, we still need to know why they have higher levels of this specific bacteria one week after the new treatment.

The untreated chicks’ incidence of illness doesn’t explain why treated chicks have lower Salmonella rates but higher levels of other bacteria. Also, we don’t know that the “other bacteria” in (D) is the same as the “other bacteria” in the stimulus.

This explains why treated chicks have higher levels of the other bacteria: without Salmonella, which normally limits their growth, the other bacteria can increase. The treatment reduces Salmonella, allowing the other bacteria to increase among treated chicks.