Biologists have noted reproductive abnormalities in fish that are immediately downstream of paper mills. One possible...

After missing the question initially and looking over the Message Board so far, I understand why C is the correct answer. However, my sticking point is that in choice D, I thought that by saying the physiological changes persisted in some fish, the answer choice was getting at the idea that the harmful hormone levels created lasting physical changes in the fish that remained even when the hormone levels returned back to normal. It made sense to me that even if dioxin only caused only a temporary problem with the hormone levels, the physical change/mutation itself may have still persisted (which is what the question asks about).