## Core Concept
Cerebrospinal fluid (CSF) analysis is a crucial diagnostic tool for various neurological conditions. The preservation of CSF samples is essential for accurate laboratory testing, including microbiological cultures, cytological examination, and biochemical analysis. Different conditions require specific preservation methods to maintain the integrity of the sample.

## Why the Correct Answer is Right
The correct answer, , implies that CSF is required to be preserved in a **plain sterile tube** or **transport medium** for microbiological examination, especially when there is a suspicion of bacterial meningitis or other infections. This method helps in preserving the viability of pathogens, such as bacteria, for culture and sensitivity testing.

## Why Each Wrong Option is Incorrect
* **Option A:** - This option is incorrect because an **EDTA tube** is used for hematological tests, such as cell counts, and not typically for microbiological cultures or routine CSF analysis.
* **Option B:** - This option is incorrect because a **sodium fluoride/potassium oxalate tube** is used for glucose testing and not for preserving CSF for microbiological cultures.
* **Option D:** - This option is incorrect because a **heparin tube** is sometimes used for certain types of testing but is not the standard for preserving CSF for routine microbiological examination.

## Clinical Pearl / High-Yield Fact
A key point to remember is that when CSF is sent for culture, it should ideally be processed promptly, but if there's a delay, it should be stored at **4°C** to slow down bacterial metabolism and preserve the viability of potential pathogens.

## Correct Answer Line
**Correct Answer: C.**