Correct Answer: A

Rationale: Pepsin is the enzyme that initiates protein digestion in the stomach. It breaks down proteins into smaller peptides, aiding in their further digestion and absorption in the intestines. Salivary Amylase (Choice B) functions in breaking down dietary carbohydrates in the mouth, not proteins. CCK (Choice C) and Secretin (Choice D) are hormones involved in the digestion of fats and carbohydrates, not proteins. Therefore, Choices B, C, and D are incorrect in the context of protein digestion in the stomach.

Correct Answer: C

Rationale: The correct answer is C: Carcinomas. Carcinomas are cancers that originate from epithelial tissues, which are the tissues lining the surfaces of organs and structures in the body. Leukemias (choice A) are cancers of the blood-forming cells, not epithelial tissues. Myelomas (choice B) are cancers that develop in plasma cells in the bone marrow, not epithelial tissues. Sarcomas (choice D) are cancers that arise from connective tissues like bone, cartilage, or muscle, not epithelial tissues. Therefore, choices A, B, and D are incorrect in the context of cancers originating from epithelial tissues.

Correct Answer: A

Rationale: In patients with stage 5 chronic kidney disease (CKD), also known as end-stage renal disease, the kidney function is significantly compromised. This severe condition is characterized by a glomerular filtration rate (GFR) of less than 15 mL/min/1.73 m², as correctly stated in choice A. Choices B, C, and D suggest higher GFR values, which are not indicative of stage 5 CKD. Specifically, a GFR of less than 30 mL/min/1.73 m² indicates stage 4 CKD, less than 90 mL/min/1.73 m² signifies stage 3 CKD, and a typical healthy individual usually has a GFR of around 125 mL/min/1.73 m², which is far above the GFR for stage 5 CKD.

Correct Answer: B

Rationale: Phospholipids are a major component of cell membranes, providing structural integrity and facilitating cell signaling. Cholesterol (choice A) is also present in cell membranes but in smaller amounts and plays a different role. Saturated (choice C) and triglyceride (choice D) are not major constituents of cell membranes.

Correct Answer: D

Rationale: The first statement is false; fluoride is not added to infant formulas due to the risk of fluorosis. The second statement is true; breast milk contains low levels of fluoride.