11. Which of the following statements about vitamins is true?

Question

BlackTom AI · Accepted Answer

Vitamins are organic micronutrients required in trace amounts for normal metabolism, growth, and maintenance of health. They cannot generally be synthesized in sufficient quantities by the body and therefore must be obtained from the diet (or produced by gut flora only in limited amounts). Vitamins fall into two biochemical categories—fat-soluble (A, D, E, K) and water-soluble (B-complex and C)—and they often act as cofactors/coenzymes or regulatory molecules rather than as direct energy sources.

Step-by-step reasoning:
1. Essential nature: Most vitamins are essential because the human body cannot synthesize adequate amounts; dietary intake prevents deficiency diseases (e.g., vitamin C deficiency → scurvy; vitamin D deficiency → rickets/osteomalacia). This supports any statement that vitamins are required and deficiency causes disease.
2. Functional role: Many vitamins (especially B vitamins) are precursors to coenzymes (e.g., niacin → NAD+/NADP+, riboflavin → FAD) that participate in metabolic reactions. This supports statements that vitamins serve as coenzymes or regulators.
3. Solubility and storage/toxicity: Fat-soluble vitamins are stored in body fat and the liver and can accumulate to toxic levels if consumed in excess; water-soluble vitamins are generally not stored and excess is excreted in urine, making toxicity less common (though possible with some B vitamins in high doses). This supports statements about differential storage and toxicity.
4. Dietary origin: Because the body relies on dietary sources, saying vitamins must be obtained from food is accurate.

Why D (“All of the above”) is correct: each individual statement (A, B, and C) describes a true attribute of vitamins—essentiality, biochemical function as coenzymes/regulators, and differences between fat- and water-soluble vitamins—so selecting “All of the above” correctly affirms all true points simultaneously.

Why selecting A, B, or C alone would be incorrect: any single option would omit other true and relevant properties; the most complete and correct choice is the one that includes all true statements. Therefore the correct answer is D.

11. Which of the following statements about vitamins is true?单项选择题

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