**Core Concept**
Skeletal maturation is a complex process involving the coordinated action of multiple hormones and growth factors. The hormone primarily responsible for regulating this process is thyroid hormone, which plays a crucial role in the development and growth of the skeletal system.

**Why the Correct Answer is Right**
Thyroid hormone, particularly triiodothyronine (T3) and thyroxine (T4), stimulates the growth and maturation of the skeletal system by promoting the differentiation and proliferation of osteoblasts, the cells responsible for bone formation. T3 and T4 also regulate the expression of genes involved in bone metabolism, including those encoding for collagen and other matrix proteins. The thyroid hormone also regulates the activity of growth factors such as insulin-like growth factor-1 (IGF-1), which further promotes skeletal growth and maturation.

**Why Each Wrong Option is Incorrect**
**Option A:** Growth hormone (GH) is involved in regulating growth and development, but it is not the primary hormone responsible for skeletal maturation. GH primarily stimulates the production of IGF-1, which in turn promotes growth, but it is not directly involved in the maturation process.
**Option B:** Parathyroid hormone (PTH) is involved in regulating calcium and phosphate homeostasis, but it is not directly responsible for skeletal maturation. PTH can influence bone growth and resorption, but its primary role is in regulating mineral ion homeostasis.
**Option C:** Calcitonin is involved in regulating calcium and phosphate homeostasis, particularly in response to high levels of calcium in the blood. It is not directly involved in skeletal maturation.

**Clinical Pearl / High-Yield Fact**
Thyroid hormone plays a critical role in regulating growth and development, and abnormalities in thyroid hormone levels can lead to growth disorders, including cretinism in hypothyroidism and acromegaly in hyperthyroidism.

**Correct Answer:** C. Thyroid hormone.