Which of the following is/are primary air pollutant$(s)$?

Rain is called acid rain when its $pH$ is below

$A$ - Micro-organisms involved in the biodegradation of organic matter in the receiving water body consume a lot of oxygen,and as a result,there is a sharp decline in dissolved oxygen in the stream from the point of sewage discharge.
$R$ - $BOD$ decreases when the dissolved oxygen amount decreases in water.

What are the various components of domestic sewage? Discuss the effects of discharging sewage into a river.

Why does fish mortality occur due to eutrophication?

Due to biomagnification,$DDT$ residues pass through the food chain rapidly because $DDT$ is .......