**Core Concept**
CSF Rhinorhoea refers to the leakage of cerebrospinal fluid (CSF) through the nose, resulting from a defect in the dura mater, which separates the brain from the nasal cavity. This condition can occur due to trauma, surgery, or congenital defects in the skull base.

**Why the Correct Answer is Right**
The most common site for CSF Rhinorhoea is the cribriform plate, which is a thin, porous bone located in the anterior cranial fossa. The cribriform plate forms part of the nasal septum and is a common site for fractures due to its thin structure and location. When the cribriform plate is fractured, it can lead to a communication between the nasal cavity and the subarachnoid space, resulting in CSF Rhinorhoea. The cribriform plate's proximity to the olfactory bulbs and the anterior ethmoidal artery also makes it a vulnerable area for trauma.

**Why Each Wrong Option is Incorrect**
**Option A:** The ethmoidal sinuses are located between the nasal cavity and the cribriform plate, but they are not the most common site for CSF Rhinorhoea.
**Option B:** The sphenoid sinus is located in the sphenoid bone, which is situated posterior to the cribriform plate, making it less likely to be the most common site for CSF Rhinorhoea.
**Option C:** The frontal sinus is located in the frontal bone, which is situated above the cribriform plate, making it less likely to be the most common site for CSF Rhinorhoea.

**Clinical Pearl / High-Yield Fact**
CSF Rhinorhoea can be a challenging diagnosis, as the symptoms may be mild and intermittent. A high index of suspicion is required, especially in patients with a history of head trauma or recent surgery.

**Correct Answer:** C. Cribriform plate.