Jhum cultivation is prevalent in $.................$.

Maximum greenhouse gases are released by

Contribution of individuals: Sunderlal Bahuguna.

Increase in concentration of a toxicant at successive trophic levels is called

Which of the following statements is correct?

How many sentences are correct?
$(1)$ $CNG$ burns most efficiently.
$(2)$ $CNG$ cannot be adulterated.
$(3)$ $CNG$ is cheaper than petrol and diesel.
$(4)$ In the $1990$s,Delhi ranked $4$th among the $41$ most polluted cities of the world.