When domestic sewage mixes with river water
(a) small animals like rats will die after drinking river water
(b) the increased microbial activity releases micronutrients such as iron
(c) the increased microbial activity uses up dissolved oxygen
(d) the river water is still suitable for drinking as impurities are only about 0.1 %

Options

A. small animals like rats will die after drinking river water
B. the increased microbial activity releases micronutrients such as iron
C. the increased microbial activity uses up dissolved oxygen
D. the river water is still suitable for drinking as impurities are only about 0.1 %

Answer

C