Recent studies have indicated that a certain type of freshwater cod has more tumors than other species of fish in the Hudson River. Long before this phenomenon was recognized, significant progress had been made in clearing the river of chemicals and other kinds of pollution thought to promote tumor growth in fish.
Which one of the following conclusions can most reliably be drawn from the statements above?
A. There is no causal link between pollution and the tumors in the freshwater cod.
B. Efforts to clear the Hudson of chemicals and other kinds of pollution have not been strong enough.
C. A sudden change in the river environment has had a drastic effect on the freshwater cod.
D. No other fish besides the freshwater cod can be harmed by chemicals and other kinds of pollution.
E. The studies mentioned provide no evidence that the number of tumors in the freshwater cod is related to the amount of pollution in the river.
