Answer: A compound is a substance in which two or more elements are combined together chemically.
Explanation: Elements present in a compound are always in a fixed proportion and can be separated only by a chemical method. For example, water is a compound composed of hydrogen and oxygen atoms in the ratio of 2:1. The chemical formula of water is H2O.
The answer is <span>The respiratory system supplies the oxygen that the cardiovascular system transports to the different cells for the production of energy.
When air enters the lungs (part of the respiratory system), it passes all way to the alveoli, the smallest functional units of the lung. There, oxygen from the air enters the capillaries, the smallest blood vessels, next to the alveoli. Once in the blood stream, the cardiovascular system transports oxygen to different cells where it is used for the energy production.</span>
the correct answer is Local backyard bird feeders without food because that is what you are keeping the same and not changing
I think the answer to this is D.
