In an area where DDT had been used extensively the population of birds declined significantly because

Options

A. earthworms in the area got eradicated
B. cobras were feeding exclusively on birds
C. many of the birds eggs laid, did not hatch
D. birds stopped laying eggs

Answer

C

Explanation

Domestic sewage contains large amount of organic matter and microbas. Suspended solids and dissolved salts are more seen in industrial waste water.
STPs require both the aerobic and the anaerobic steps.
When Aerobic bacteria act break down the organic matter of sewage they consume oxygen. The BOD of the sewage goes on decreasing with the decrease in organic matter. BOD is a measure of the amount of organic matter it does not indicate the presence of bacteria. Thus first three options are incorrect.