**Core Concept**
The vertebral column exhibits four types of curves, which are primary and secondary curves. Primary curves are present at birth and are concave anteriorly, whereas secondary curves develop later in life due to postural habits and are concave posteriorly.

**Why the Correct Answer is Right**
The secondary curves in the vertebral column are found in the thoracic and sacral regions. These regions develop concavity posteriorly due to the effects of gravity and postural habits. The thoracic region, which is the primary site of secondary curves, exhibits a concavity posteriorly due to the weight of the head and the anteriorly directed forces exerted by the abdominal contents and pelvic floor. This results in a posterior concavity, which is a characteristic feature of secondary curves.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option does not specify the region of the vertebral column, making it an ambiguous choice. The thoracic and sacral regions are the primary sites of secondary curves, and specifying one of these regions would be more accurate.
* **Option B:** This option does not provide any information about the direction of curvature. Secondary curves are characterized by a concavity posteriorly, and simply stating "secondary curves" does not provide enough information to determine the correct answer.
* **Option C:** This option is incorrect because the lumbar region is a primary site of curvature, not a secondary curve. The lumbar region is concave anteriorly, which is a characteristic feature of primary curves.

**Clinical Pearl / High-Yield Fact**
Remember that the vertebral column exhibits four types of curves: primary and secondary curves. The primary curves are present at birth and are concave anteriorly, whereas secondary curves develop later in life due to postural habits and are concave posteriorly.

**Correct Answer:** C.