What causes eutrophication and how does this occur?

The growth of algal bloom in the nearby water bodies of the agricultural fields due to excess of the nutrients is called as eutrophication.

This is caused due to the excessive use of fertilizers in the fields. The excess of fertilizers gets run off to the nearby water bodies which lead to the growth of the algae.

The algae forms a layer on the upper surface of the water that decreases the oxygen concentration in the water that adversely affects the life of other aquatic life forms in it.

the correct option is option d

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".