Correct Answer: D

Rationale: The primary reason for prescribing testosterone therapy for osteoporosis in men is to restore testosterone levels, not specifically to increase bone density. Testosterone plays a crucial role in maintaining bone density, so by restoring testosterone levels, it indirectly helps in maintaining bone density. Choices A and B are partially correct but do not address the primary reason for testosterone therapy in this context. Choice C is incorrect as the main focus of testosterone therapy in osteoporosis treatment is not related to enhancing sexual performance.

Correct Answer: B

Rationale: The correct answer is B: 'Use of nitrates.' Sildenafil (Viagra) is contraindicated in patients taking nitrates due to the risk of severe hypotension. Nitrates and sildenafil both act as vasodilators, and their combined use can lead to a dangerous drop in blood pressure. Choices A, C, and D are incorrect because having a history of hypertension, using antihypertensive medications, or having a history of peptic ulcer disease are not key contraindications for sildenafil use.

Correct Answer: A

Rationale: The correct answer is Sarcoptes scabiei. Sarcoptes scabiei is a parasitic mite that causes scabies, characterized by small red skin lesions and intense itching. Pediculosis corporis (choice B) refers to body lice, which do not cause the specific symptoms described. Pediculosis pubis (choice C) is caused by pubic lice and presents differently from the symptoms described. Toxoplasma gondii (choice D) is a parasite that causes toxoplasmosis, but it does not typically manifest with small red skin lesions and itching.

Correct Answer: C

Rationale: Antigens are the correct answer as they are the molecules that trigger the immune response by binding to specific B or T cells. This binding activates these cells, leading to their proliferation and differentiation to fight off the antigen. B cells and T cells are the responders to antigens, not the initiators of clonal selection. Lymphocytes is a broad term encompassing both B and T cells, so it is not the specific factor responsible for initiating clonal selection.

Correct Answer: D

Rationale: In third-degree burns, infection is a major concern due to the extensive damage to the skin. Monitoring for infection is crucial. Choice A is incorrect because third-degree burns often require skin grafts due to the severity of the injury. Choice B is incorrect as loss of sensation is more common in nerve damage and not necessarily in burns. Choice C is incorrect because while elevation can help with swelling in minor burns, it is not the most critical concern in third-degree burns.