Why is the percentage of food eaten a good number to use

A percentage compares the number of birds in the flock to the total number of birds in all flocks.

If the percentage is high, the flock is more successful, so the flock should grow.

If the percentage is low, the flock is struggling to eat, so the flock should shrink

Explanation:

answer; (b); it becomes

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.