**Core Concept**
Cerebrospinal fluid (CSF) must be preserved in a controlled environment to maintain its integrity for forensic and diagnostic purposes. The optimal storage temperature balances microbial inhibition and preservation of biochemical composition.

**Why the Correct Answer is Right**
CSF is stored at **4°C** to prevent bacterial growth while minimizing degradation of proteins and other biomarkers. This temperature is sufficient to slow microbial activity without causing chemical breakdown of CSF components. It is also compatible with standard laboratory handling and transport protocols in forensic settings.

**Why Each Wrong Option is Incorrect**
Option B: **-20°C** is too cold and may cause ice crystal formation, altering CSF structure and leading to false test results.
Option C: **Room temperature** allows rapid bacterial growth and degradation, making it unsuitable for forensic storage.
Option D: **-70°C** is typically used for long-term storage of blood or tissue samples, not routine CSF, and may lead to freeze-thaw damage and loss of analytes.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, CSF must be stored at **4°C** and processed within 24 hours to ensure accurate analysis. Never store CSF at room temperature or below 0°C without proper monitoring.

✓ Correct Answer: A. 4degC