Final answer:
Conditionally essential nutrients become vital due to specific bodily states or medical conditions, such as PKU, where tyrosine becomes essential due to the body's inability to synthesize it from phenylalanine.
Step-by-step explanation:
Conditionally essential nutrients are nutrients that are normally not essential but become vital under certain conditions or in specific situations, such as illness, stress, or trauma. An example of a conditionally essential nutrient is the amino acid tyrosine. Tyrosine is usually produced by the body from another amino acid called phenylalanine. However, in individuals with the genetic disorder phenylketonuria (PKU), they lack the enzyme needed to convert phenylalanine to tyrosine, making tyrosine an essential nutrient that needs to be obtained from the diet.
For another example, argument A, which erroneously states that essential nutrients are not necessary for proper body function, is incorrect. Instead, as mentioned in the provided information, essential nutrients are indeed required but cannot be synthesized by the body in sufficient amounts, and so they must be consumed through diet. An example of such essential nutrients would include Vitamins A and K, where Vitamin A is critical for vision and Vitamin K for blood clotting.