What is $DDT$?

Black foot disease is caused by the toxicity of which of the following?

Concentration of $DDT$ in small fishes is..... (in $, ppm$)

Assertion $(A)$: Pollution is always caused by human activities.
Reason $(R)$: Pollution is not different from contamination.

In almost all major Indian metropolitan cities like Delhi,the major atmospheric pollutants are .........

Which of the following problems in humans is not caused by noise pollution?