Oxygen molecules come from
air
Starches
Proteins
food

air

Explanation:

The main source of oxygen molecules is the air around us. Air is made up of 21% of oxygen gas which is the second most abundant gas found in the atmosphere.

Starch, Proteins and food are all made up of complex organic molecules. Air is a mixture of many gases. Gaseous exchange is made possible when air supplies oxygen and takes carbon dioxide away. Oxygen is an essential gas in the metabolic process of animals.

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The independent variable is the type of music.the dependent variable is the pulse rate.the intervening variable is the age of the subject.if the mother does not like rock, her pulse is likely to not increase.the same might be true for the sister.the friend may like rap and gets excited.to establish cause/effect relationship, all of the subjects must be consistent.hope i .