The multiple choice questions have five answer choices — one (and only one) is correct in each case.
A stream is free of pollutants within a few miles downstream of a point at which a small amount of sewage is being dumped into it. This is most likely the result of
Select an Answer
The correct answer is decomposition, (E). Decomposition breaks down organic material such as sewage. Succession of vegetation types (A) does not explain this process. Eutrophication (B) might well result from the dumping of sewage into a body of water, but does not explain the observation that the stream is free from pollutants a few miles downstream. Evaporation (C ) would result in the loss of water from the stream but not the loss of pollutants. Photosynthesis (D) takes place in aquatic plants and algae, sometimes using the products of decomposition, but it does not result in the breakdown of organic material.