It is one of the beginning compounds.
This is the answer for many reasons. First off, it is not one of the ending compounds. It is only the end compound for photosynthesis. Second, it does not react to water as that is yet again photosynthesis. It does not react with carbon dioxide as carbon dioxide is what initially creates oxygen within cellular respiration.
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Answer:
Because you body is introduced to the virus, it is familiar to it and can build up an immunity to the weakened form so when the actual virus invades, your body know what to do.
Explanation: