**Core Concept**
Normal cerebrospinal fluid (CSF) pressure is a critical parameter in neurology and neurosurgery, reflecting the balance between CSF production and reabsorption. The CSF pressure is typically measured in millimeters of water (mmH2O) or centimeters of water (cmH2O) and is influenced by the dynamics of CSF circulation and the intracranial pressure.

**Why the Correct Answer is Right**
The normal CSF pressure ranges from 50 to 180 mmH2O, with an average value of around 120 mmH2O. This pressure is determined by the balance between CSF production in the choroid plexus and reabsorption through the arachnoid villi. The CSF pressure is also influenced by the intracranial pressure, which is determined by the volume of blood in the cranial cavity, the elasticity of the cranial vault, and the cerebrospinal fluid production and reabsorption rates.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it is too low and does not reflect the normal range of CSF pressure.
**Option B:** This option is incorrect as it is too high and does not reflect the normal range of CSF pressure.
**Option C:** This option is incorrect as it is not within the normal range of CSF pressure and may indicate an underlying pathology.

**Clinical Pearl / High-Yield Fact**
It is essential to note that CSF pressure can be influenced by various factors, including posture, age, and underlying medical conditions. A decrease in CSF pressure may indicate low CSF volume or increased intracranial pressure, while an increase in CSF pressure may indicate increased CSF production or obstruction of CSF reabsorption.

**Correct Answer: D. 120 mmH2O**