Name three different freshwater ecosystems. name two aquatic ecosystems that are not made of solely freshwater and no freshwater.

The circles, or orbits, for electrons are called energy levels. each level can hold only a certain number of electrons. add electrons to each level until you can't add any more. how many electrons can each level hold?

As a small change in a person's dna can cause a genetic disorder

Which was most likely an effect on society that resulted from improvements in blood handling during world war i and world war ii?