Suppose an experiment is done to see if a dietary supplement affects the weight gain of chickens. So the variables which need to be controlled - where the chickens are kept, the availability of water and temperature of the surroundings.
Dietary supplements are approved by FDA which come in the form of capsules, pills, powders, gel capsules, tablets, extracts, or liquids. They generally contain vitamins, minerals, fibre, herbs, amino acids, other plants or enzymes. The ingredients in dietary supplements are sometimes added to foods and drinks.
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