As an environment changes, and some organisms have a higher fitness than others, natural selection acts directly on what.

a. existing variations
b. genetic material
or
d. individual organisms

Many organs are involved in the processes of keeping the blood and the body clean. when poisonous or harmful substances are in the blood, they are absorbed by the and released in a less harmful form. when wastes are present in the blood, they are filtered out and removed from the body by the

In which state was more than 100 billion tons of coal mined in 2005?

What is the main fuel source for the work of the cell