Downstream of a sewage outlet, fish die because microbes consume the:
ADissolved oxygen
BDissolved salts
CIncoming sunlight
DRiver bed sand
Answer & Solution
Correct answer: A. Dissolved oxygen
1. Microbes multiply on the organic matter.
2. They use up oxygen as they work.
3. Dissolved oxygen falls sharply and fish die.
_Source: NCERT Class 12 Biology, Chapter 16, Environmental Issues._
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