irregular polygon is any polygon that is not a regular polygon. It can have sides of any length and each interior angle can be any measure. They can be convex or concave, but all concave polygons are irregular since the interior angles cannot all be the same.
1-PH.....
2-Turbidity......
The correct answer is D.
A keystone specie refers to a plant or animal which play very important roles in the way a particular ecosystem functions. Without the keystone specie the ecosystem will be totally different or even cease to exist, thus keystone species have strong influence on the ecosystems in which they exist. Most of the time a keystone specie is a dominant predator whose removal allow a prey population to increase dramatically in size and thus reduce the overall diversity in that particular ecosystem.
The answer to this is Gonads.