A river's width and depth increases as more water is added from tributaries.
Answer:
[a] varies in its characteristics according to local environmental circumstances
[b] becomes common within a species through natural selection
[d] tends to promote the well being of an organism in its natural or social environment
Explanation:
The adaptive traits in the living organisms have a simple basic role, that is to make the organism better suited for survival in its environment. The adaptive traits come in all sorts of different shapes, be it some that are manifested in the physical appearance or in the behavior of the organisms. Adaptive traits can be increased speed, prolonged neck, living in a groups, developing thorns and many more. This type of traits occur when the organisms face increased competition or when the environment in which they live starts to change, so in order for them to survive, they start to develop traits that will make them better suited for the new conditions and more competitive. The main principle through which the adaptive traits are transferred and rapidly increase in a population is through natural selection, as the organisms choose the ones that have advantageous traits for their mates, while they live aside the others.
Erosion of farmland, overuse of both surface and groundwater, dwindling supplies of finite fossil fuels, and escalating extinction of plant and animal species imperil the ability of the earth's resources to meet the needs of such enormous numbers of humans. The food situation worldwide is becoming critical
