Ancestors of giraffes with shorter necks could not reach branches high up in trees for food. this led to for longer necked giraffes.

Directional Selection.

Explanation: Earlier the ancestors of the giraffe had shorter neck as compared to the giraffe of the present time.

They were not able to access the plants that lied at a higher height.They was some changes in the phenotype of the giraffe in which the giraffe has long necks to access the plants at height.

In directional selection the extreme form is preferred over other traits. Example: The long neck giraffe were selected over short neck.

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.

oxygen +1 most likely