Correct Answer: A

Rationale: Food products fortified with dietary vitamins and minerals have had the greatest impact on combating nutrition deficiencies in developing countries. By fortifying food products with essential nutrients such as vitamins and minerals, it becomes easier to address specific deficiencies in populations that may not have access to a diverse range of foods. This innovation has been particularly impactful in addressing common deficiencies like vitamin A, iron, zinc, and folic acid, improving overall health outcomes in populations with limited access to nutrient-rich foods. Choices B, C, and D are incorrect. Integrated statistical models of fish populations, advances in microscopy, and refrigerated train cars, while important in their own right, do not directly address combating nutrition deficiencies in developing countries as effectively as food fortification with essential nutrients.

Correct Answer: B

Rationale: The small intestine is the primary site where the absorption of nutrients from digested food occurs. Its large surface area, specialized cells, and villi play key roles in maximizing nutrient absorption, making it the structure in the digestive system that absorbs the most nutrients. The stomach's main function is to break down food with acid and enzymes, not absorb nutrients. The large intestine primarily absorbs water and electrolytes, not nutrients. The esophagus is a muscular tube that connects the throat with the stomach and does not play a role in nutrient absorption.

Correct Answer: C

Rationale: Option C, 'It helps cushion the heart against jarring motions,' is NOT a major function of the respiratory system in humans. The primary functions of the respiratory system include gas exchange, regulation of blood pH, and vocalization. The respiratory system does not play a role in cushioning the heart; that function is primarily carried out by the pericardium and other protective structures around the heart. Choices A, B, and D are major functions of the respiratory system in humans. Choice A refers to the respiratory system's role in gas exchange, Choice B highlights its involvement in regulating blood pH, and Choice D points out its responsibility for vocalization.

Correct Answer: B

Rationale: The correct pathway of deoxygenated blood in our body involves blood returning from the body, entering the right atrium, then passing to the right ventricle, and eventually reaching the lungs for oxygenation. This sequence ensures that deoxygenated blood is pumped to the lungs, where it receives oxygen and releases carbon dioxide before circulating back to the body. Choices A, C, and D are incorrect because they do not follow the actual path of deoxygenated blood in the circulatory system.

Correct Answer: C

Rationale: The correct answer is the liver. The liver is responsible for producing bile, regulating blood sugar levels, and detoxifying the blood. Bile produced by the liver is stored in the gallbladder. The pancreas primarily functions in digestion by producing enzymes and insulin, while the stomach is mainly involved in breaking down food through the secretion of gastric juices.