In the following passage, The issue of growing environmental pollution should be considered as one of (1) ______ importance.

In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.
The issue of growing environmental pollution should be considered as one of (1) ______ importance. The environment (2)______ the air we breathe, the water we drink, the trees and plants that (3) ______ food for us and the animal kingdom. All of these together form the circle of life on earth. Pollution is a process by which natural elements of the earth are negatively (4) ______, causing harm and (5) ______ to this circle of life.
Q.Select the most appropriate option to fill in blank no. 1.