Which is the main causative factor of desertification?

What is the raw material for polyblend?

$A$ greenhouse is primarily used to grow plants during the $..........$ season.

Among the $X$ most polluted cities in the world,Delhi ranked at $Y$ position. Identify $X$ and $Y$.

Given below are two statements.
Statement $I$ - Algal blooms impart a distinct color to the water bodies.
Statement $II$ - Some bloom-forming algae are extremely toxic to fishes but not to human beings and other animals.
In the light of the above statements,select the correct option:

$A$: Polyblend is a fine powder of recycled modified plastic.
$R$: The blend of polyblend and bitumen helps to increase road life by a factor of three.