The human skeleton consists of which of the following?

Correct Answer: B

Rationale: The skeleton comprises axial (skull, spine, ribs) and appendicular (limbs, girdles) parts. Other options omit or misgroup components. Answer is B, per the document.

Correct Answer: C

Rationale: Abduction moves a limb away from the midline (e.g., thigh laterally). Extension straightens, adduction moves toward, flexion bends. Answer is C, per the document.

Correct Answer: C

Rationale: Bone is living tissue with cells, blood vessels, and marrow—most blood cells are made in marrow (A), it stores minerals like calcium (B), and it protects/supports organs (D). 'Bone is a dry and non-living supporting structure' is incorrect due to its living nature.

Correct Answer: D

Rationale: Compact bone is dense with osteons, while spongy bone is porous with trabeculae—differing in cell arrangement, not marrow type, material (both hydroxyapatite), or cell size. 'They have different arrangement of bone cells' is correct.

Correct Answer: A

Rationale: Osteoporosis involves excessive bone resorption. Cortisol (from the adrenal glands) stimulates osteoclast activity, which breaks down bone tissue, potentially leading to porosity if unbalanced. Estrogen supports osteoblasts (bone formation), thyroid hormone can increase both formation and resorption but isn’t primarily linked to osteoporosis, and thyrocalcitonin (calcitonin) inhibits osteoclasts, reducing bone loss.