To identify the assumption, we need to find the unstated premise that the argument relies on. The argument claims that water pollution is the primary cause of the decline in the salmon population and that reducing pollution will lead to a recovery.
A) There are no other significant factors contributing to the decline in the Pacific salmon population.This is a strong contender because if other significant factors are contributing to the decline, addressing only water pollution might not lead to a recovery in the salmon population.
B) The level of water pollution in the rivers where the salmon spawn has increased significantly in recent years.
While this might support the argument, it is not an assumption the argument depends on. The argument could still hold if pollution levels were always high.
C) The salmon population has declined in all rivers where they spawn, not just in those with increased pollution levels.This weakens the argument rather than supports it because it suggests factors other than pollution could be responsible for the decline.
D) Reducing water pollution in the rivers where salmon spawn will not have any adverse effects on other species of fish.This is irrelevant to the argument about the salmon population recovery.
E) The pollutants in the rivers are directly harmful to the reproductive processes of the Pacific salmon.This is essential to the argument. If the pollutants are not directly harmful, reducing pollution might not lead to a recovery in the salmon population.
The correct answer is:E) The pollutants in the rivers are directly harmful to the reproductive processes of the Pacific salmon.