Nearly one billion dollars a year are spent on clearing sediment from streams and lakes in the United States.

Which is the most common source of this sediment?

A. productive farmland that is over-irrigated

B. waste dumped by mining industries into the waterways

C. hilly areas where protective vegetation has been removed

Answer: Option C

Explanation: Hills are the most common source of sediments because they lack vegetation. Plants and trees hold the soil and thus prevent erosion of soil layer with water. The sediments from the hilly areas get carried by rain water or runoff, and add to the water bodies, like lakes and streams.

Waste from mining industries don’t have sediments in their waste, so option B is incorrect.

Option A is incorrect because over-irrigation will not affect the soil layer, as it is firmly held by the roots of the crops.

The answer is C) Hill areas where protective vegetation has been removed ...