When was the Bharat Stage $IV$ emission standard implemented for vehicles in the city?

$A$: High concentration of atmospheric $SO_2$ and $NO_x$ causes acid rain.
$R$: It causes damage to foliage and growing points of plants.

Contour farming is usually employed in

Assertion : Methane,a component of greenhouse gases,contributes about $20$ percent to global warming.
Reason : The introduction of multi-point fuel injection engines in automobiles has decreased methane content in the exhausts.

Eutrophication is caused by

Polyblend is mixed with $\underline {i}$ and is used to lay $\underline {ii}$.