Answer:
D). Turbidity, because a decrease in water clarity would indicate and increase in soil erosion.
Step-by-step explanation:
The last option most aptly describes the direct effect of soil erosion i.e. 'turbidity' which would assist the students in discovering the impact produced by the construction project built on the river. The turbidity is characterized as the 'unit of measuring the transparency of a fluid or the state of being unclear and lesser sediments being disturbed' which causes a significant fall in clarity of the water which signals that there has been a rise in erosion of soil after the construction of the project. Thus, option D is the correct answer.