The erosion of topsoil, and the run-off of fertilisers and pesticides into water bodies, are examples of:

Correct answer: (a) Negative and positive pollution

Explanation

In soil pollution, "negative" and "positive" do not mean bad and good:

• negative pollution is the removal of something useful from the soil. Erosion of topsoil removes the fertile top layer;
• positive pollution is the addition of harmful substances. The run-off of fertilisers and pesticides adds chemicals that then reach water bodies.

So the two are examples of negative and positive pollution, in that order.