Correct Answer: C

Rationale: The primary function of protein in the diet is to build and repair tissues. Proteins are essential for the growth, maintenance, and repair of body tissues like muscles, skin, and organs. While proteins can be a source of energy, their primary role is not to supply energy, making choice A incorrect. Choice B is also incorrect as proteins do not synthesize vitamins; rather, they are essential nutrients themselves. Choice D is inaccurate because glycogen is a form of stored glucose in the body, not a function of protein.

Correct Answer: D

Rationale: The correct answer is D. The stomach is protected from gastric acid by a thick mucus lining that acts as a physical barrier, preventing the acid from eroding the stomach walls. Enzymes in the stomach help with digestion but do not play a significant role in protecting the stomach from acid damage, so choice A is incorrect. While some bacteria in the stomach can be beneficial, they do not primarily protect the stomach from gastric acid, making choice B incorrect. Bicarbonate, a base, can neutralize acid, but it is not the primary defense mechanism against gastric acid in the stomach, so choice C is also incorrect.

Correct Answer: A

Rationale: Short-chain fatty acids are the preferred fuel for the cells lining the colon. They provide energy and support gut health by serving as a fuel source for these cells. Long-chain fatty acids are not the preferred fuel for colon cells as they are harder to digest and absorb in this part of the digestive system. Amino acids are the building blocks of proteins and not the primary energy source for colon cells. Glucose is the main energy source for most cells in the body, but colon cells prefer short-chain fatty acids.

Correct Answer: D

Rationale: Short-chain fatty acids are the most water-soluble and are more easily absorbed into the bloodstream. Very long, long, and medium-chain fatty acids are less water-soluble and are absorbed at a slower rate compared to short-chain fatty acids. Therefore, the correct answer is D.

Correct Answer: C

Rationale: The correct answer is 1500 mg to 3000 mg per day. This is the level of sodium restriction typically recommended for heart failure patients. It helps manage fluid retention and reduce blood pressure, which are both crucial in treating heart failure. A sodium intake of less than 500 mg per day (Choice A) might be too restrictive and is not typically recommended. Similarly, an intake of 1000 mg to 1500 mg per day (Choice B) falls short of the recommended range. Lastly, an intake of 3000 to 3500 mg per day (Choice D) exceeds the recommended upper limit, potentially exacerbating fluid retention and high blood pressure.