C is the proper answer. They have been reduced by using unleaded gasoline because lead can harm the air and water we breathe, so using less of it will help reduce the pollution being caused by it.
From simplest to most complex it would be atom, molecule, cell, tissue, organ, organ system. Hope this helps!
A new species can develop in just a few generations
Yes! You're right. It is evaporation. Since evaporation is a cooling process, it takes the heat of a surface away. - releasing heat