Eutrophication is caused by a. an increase in nutrients b. a decrease in nutrients c. the introduction of new species of animals d. the introduction of new species of plants

a. an increase in nutrients

Explanation:

Eutrophication is caused by an increase in nutrients.

Option A

Explanation:

Eutrophication can be defined as a phenomenon which takes place due to excess of nutrient in the water bodies.

The agricultural runoff that travels from the agricultural fields to the nearby  water bodies. These run off contains nitrogen and potassium which increases the growth of algal bloom in water.

This algal bloom covers the water surface and decreases the oxygen concentration in the water and kills the aquatic animals found in water.

Hence, the correct answer is option A

multiplying and dividing the two decimals and the eqations by the same number of the overalls