they cannot happen at the same time
A chain of amino acids folded and twisted into a molecule
Answer: Classified as a theory.
Explanation: The dictionary definition of theory is a system of ideas that are used to logically explain something. It also says that they are also based off of something not entirely connected to the thing the theory is being made about.
Because the idea that the universe has expanded explains such a large number of observations, which in turn leads to more predictions and therefore more observations that support it, this becomes your system of ideas. Because this system was based off of the aforementioned observations in the first paragraph, this proves that it is best classified as a theory.
The respiratory system works with the digestive and circulatory systems to make cellular respiration possible. During cellular respiration, your cells use oxygen and glucose to release energy. Carbon dioxide is a waste product of the process. Carbon dioxide must be removed from cells.
Info from: Google lolz.