Correct Answer: B

Rationale: The correct answer is B: Underexcretion of uric acid. In gouty arthritis, the crystallization within the synovial fluid of the affected joint is caused by the underexcretion of uric acid, leading to the accumulation and subsequent crystallization of urate crystals. Choice A, destruction of proteoglycans, is incorrect as it is not directly related to the crystallization process in gouty arthritis. Choice C, overexcretion of uric acid, is incorrect because gout is primarily associated with underexcretion or decreased excretion of uric acid rather than overexcretion. Choice D, increased absorption of uric acid, is also incorrect as the primary issue in gouty arthritis is the body's inability to properly eliminate uric acid.

Correct Answer: B

Rationale: Postoperative adhesions are a common cause of mechanical small intestine obstruction. Adhesions can form after abdominal surgery, causing bands of scar tissue that may twist or pull the intestines, leading to obstruction. This is a more common cause compared to infection, tumors, or foreign bodies. Infection may lead to inflammation but is not a typical cause of mechanical obstruction. Tumors and foreign bodies can cause blockages but are less common than postoperative adhesions.

Correct Answer: D

Rationale: The correct answer is 'Low-density lipoprotein (LDL) receptor mutation with defects in breakdown.' Primary hypercholesteremia is mainly caused by mutations in the LDL receptor, leading to impaired clearance of LDL cholesterol from the blood. This results in high levels of LDL cholesterol in the bloodstream. Choices A, B, and C are incorrect because they do not directly relate to the primary cause of primary hypercholesteremia.

Correct Answer: B

Rationale: Dehydration is more likely to occur in a 50-year-old man who is morbidly obese due to the increased risk of conditions like diabetes and heart disease that can lead to fluid imbalances. Being morbidly obese can also strain the body's systems, increasing the need for water. The other choices are less likely to experience dehydration as a primary concern. While being a bodybuilder may require strict hydration practices, dehydration is more prevalent in individuals with conditions like obesity.

Correct Answer: C

Rationale: Osteosarcoma is an aggressive bone tumor that most commonly arises in the bone marrow of long bones, such as the femur or tibia. Choice A is incorrect as osteosarcoma is not a slow-growing tumor but rather a fast-growing one. Choice B is incorrect as osteosarcoma is not typically solitary but can involve multiple lesions. Choice D is incorrect as osteosarcoma primarily affects the medullary (marrow) cavity of bones, rather than infiltrating the trabeculae in spongy bone and surrounding tissue.