**Core Concept**
The skeletal convexity of the skull is a critical aspect of neurosurgical and craniofacial anatomy. The three landmarks that determine skeletal convexity are essential for identifying cranial deformities, planning surgical procedures, and understanding the biomechanics of cranial fractures.

**Why the Correct Answer is Right**
The three landmarks that determine skeletal convexity are the glabella, the nasion, and the inion. The glabella is the area between the eyebrows, where the frontal bone meets the nasal bone. The nasion is the point where the nasal bone meets the frontal bone, and the inion is the external occipital protuberance, which is the bony prominence at the back of the skull. These three landmarks are used to measure the cranial index, which is a ratio of the width of the skull to its length. By analyzing these landmarks, surgeons and radiologists can assess the skeletal convexity of the skull and identify potential issues.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify any valid landmarks for determining skeletal convexity. The landmarks provided in this option do not have any established significance in craniofacial anatomy.
* **Option B:** This option is incorrect because it does not mention the glabella, which is a critical landmark for determining skeletal convexity. Without the glabella, the measurement of skeletal convexity would be incomplete.
* **Option C:** This option is incorrect because it does not include the inion, which is a key landmark for determining skeletal convexity. The inion is essential for measuring the cranial index and assessing the shape of the skull.

**Clinical Pearl / High-Yield Fact**
The three landmarks for determining skeletal convexity (glabella, nasion, and inion) should be remembered as "GNI" to help students recall them easily. This mnemonic can be useful for remembering the correct landmarks in a high-pressure exam setting.

**Correct Answer: C. The glabella, the nasion, and the inion.**