MCQ
When domestic sewage mixes with river water:
  • A
    Small animals like rats will die after drinking river water.
  • B
    The increased microbial activity releases micro nutrients such as iron.
  • 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

Correct option: C.
The increased microbial activity uses up dissolved oxygen.

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