Correct Answer: C

Rationale: Natural killer cells are a type of lymphocyte that plays a crucial role in recognizing and eliminating virus-infected cells and cancerous cells. Neutrophils (Choice A) are a type of white blood cell involved in fighting infections, mainly through phagocytosis. Macrophages (Choice B) are another type of white blood cell that engulfs and digests cellular debris and pathogens. Langerhans cells (Choice D) are a type of dendritic cell found in the skin and mucosa, primarily involved in antigen presentation.

Correct Answer: C

Rationale: The correct answer is C. Medroxyprogesterone should be taken at the same time each day to maintain consistent hormone levels and effectiveness. Taking it at different times can lead to hormonal fluctuations and reduced medication efficacy. Choice A is incorrect because medroxyprogesterone does not need to be taken with food to prevent nausea. Choice B is incorrect as medroxyprogesterone is typically taken continuously rather than intermittently. Choice D is incorrect because side effects should be reported to the healthcare provider for further evaluation and management, not automatically leading to discontinuation of the medication.

Correct Answer: B

Rationale: Emotional stress can trigger a relapse in multiple sclerosis by exacerbating symptoms. While taking an over-the-counter multivitamin and getting a flu shot are generally safe, they are not typically known to trigger MS relapses. Engaging in strenuous physical activity, if done carefully, can actually have benefits for individuals with MS by improving strength and mobility, so it is less likely to be the cause of a relapse.

Correct Answer: B

Rationale: The correct answer is B: 'Do not take more than one dose in a 24-hour period.' It is essential for the nurse to emphasize this instruction to prevent potential adverse effects from taking multiple doses of sildenafil. Choice A is incorrect because sildenafil should be taken approximately 30 minutes to 4 hours before sexual activity, not specifically 1 hour before. Choice C is important but not the priority; while vision or hearing loss are potential serious side effects of sildenafil, the immediate concern should be focused on dose frequency. Choice D is incorrect as sildenafil can be taken with or without food.

Correct Answer: B

Rationale: Normal changes associated with aging include a slowed metabolic rate and decreased brain weight. Option A, 'Improved blood flow,' is incorrect as aging is generally associated with reduced vascular health rather than improved blood flow. Option D, 'Improved nerve fiber conduction,' is incorrect as aging typically leads to a decline in nerve function rather than improvement.