Correct Answer: A

Rationale: The correct answer is A: Forming neurotransmitters. Methionine, tyrosine, and tryptophan are important amino acids involved in the production of neurotransmitters in the body. Neurotransmitters are chemical messengers that transmit signals across nerve cells, influencing various functions such as mood, memory, and muscle control. Choices B, C, and D are incorrect because these amino acids do not primarily play a role in blocking protein breakdown, increasing insulin and thyroxine production, or decreasing energy expenditure.

Correct Answer: B

Rationale: The correct answer is B: Plant sterols. Plant sterols can reduce cholesterol absorption by competing with cholesterol for absorption sites. Vitamin K, choice A, does not have a significant impact on cholesterol absorption. Trans fats, choice C, are known to increase cholesterol levels rather than decrease absorption. Phospholipids, choice D, play a role in cell structure and are not directly involved in reducing cholesterol absorption.

Correct Answer: C

Rationale: Vitamin B12 is primarily found in animal-derived foods like meats. Choices A, B, and D are incorrect as whole grains, nuts, and legumes do not naturally contain significant amounts of Vitamin B12. Therefore, the correct answer is 'C: Meats.'

Correct Answer: A

Rationale: Dextrins are a type of polysaccharides formed during the breakdown of starch. Choice A is correct because dextrins are indeed polysaccharides, not the end products of starch digestion (Choice B). They are not formed in the liver (Choice C) nor rapidly excreted (Choice D).

Correct Answer: C

Rationale: Chylomicrons are the lipoproteins responsible for transporting dietary fat from the intestines to various tissues, including the liver. VLDL carries lipids synthesized in the liver, LDL transports cholesterol to tissues, and HDL helps transport cholesterol away from tissues to the liver for excretion. Therefore, in the context of carrying fat from a meal just consumed to the liver, chylomicrons are the correct choice.