Correct Answer: A

Rationale: The correct answer is A: Active artificial immunity. This is because the person's immune system is actively stimulated by the vaccine to produce antibodies against Covid-19. It is considered artificial because it is acquired through vaccination rather than natural exposure to the disease. B: Active natural immunity is incorrect because it refers to immunity acquired through natural exposure to the disease. C: Passive natural immunity is incorrect because it refers to temporary immunity passed from mother to baby through breast milk or placenta. D: Passive artificial immunity is incorrect because it refers to receiving pre-formed antibodies, such as through an injection of antibodies rather than the body producing them itself.

Correct Answer: C

Rationale: The correct answer is C: Cells die. In Alzheimer's disease, there is a progressive degeneration of brain cells, leading to cell death. This results in a loss of important brain functions such as memory, cognition, and eventually, bodily functions. The atrophy of the brain stem (choice A) is not a characteristic feature of Alzheimer's. Fluid buildup (choice B) is not a primary mechanism of the disease. Tissue swelling (choice D) is not typically associated with the progression of Alzheimer's; rather, there is a gradual loss of brain tissue due to cell death.

Correct Answer: B

Rationale: The correct answer is B: Administer opioid analgesics to alleviate abdominal pain and discomfort. Opioid analgesics are effective in managing severe pain associated with malignant bowel obstruction. By providing adequate pain relief, the patient's comfort and quality of life can be significantly improved. Choice A is incorrect because initiating bowel rest and maintaining the patient in a semi-Fowler's position may not effectively address the severe pain and discomfort experienced by the patient. Choice C is incorrect as surgical intervention in this scenario may not be appropriate or feasible due to the advanced stage of cancer and the presence of malignant bowel obstruction. Choice D is incorrect as antiemetic medications primarily target nausea and vomiting, which may not be the primary symptoms of concern in this case. Focusing on pain management should be the priority.

Correct Answer: B

Rationale: The correct answer is B: Acute glomerulonephritis. Glomerulonephritis is characterized by inflammation of the glomeruli in the kidneys, leading to symptoms like hematuria (blood in urine), proteinuria (excess protein in urine), and hypertension (high blood pressure). Acute tubular necrosis (A) involves damage to the renal tubules, not the glomeruli. Chronic kidney disease (C) refers to long-term kidney damage and may not always present with the classic symptoms mentioned. Nephrotic syndrome (D) involves excessive protein loss in urine but may not always involve inflammation of the glomeruli.

Correct Answer: A

Rationale: The correct answer is A: Central retinal artery occlusion. This condition presents with sudden-onset, painless vision loss, cherry-red spot at the macula due to lack of blood flow, and attenuated retinal vessels. The cherry-red spot is due to the transparency of the fovea when there is ischemia in the surrounding retina. Central retinal vein occlusion (B) presents with sudden vision loss accompanied by retinal hemorrhages and dilated tortuous veins. Retinal detachment (C) typically presents with sudden flashes, floaters, and a curtain-like visual field defect. Acute angle-closure glaucoma (D) presents with severe eye pain, blurred vision, halos around lights, and a fixed mid-dilated pupil.