**Core Concept**
Tubercular meningitis (TBM) is a severe infection of the central nervous system (CNS) caused by Mycobacterium tuberculosis. The cerebrospinal fluid (CSF) analysis is crucial in diagnosing TBM, and various parameters are altered in this condition. The CSF findings in TBM can help differentiate it from other forms of meningitis.

**Why the Correct Answer is Right**
The CSF findings in TBM include elevated protein levels, decreased glucose levels, increased lymphocyte count, and elevated adenosine deaminase (ADA) activity. The decreased glucose levels are due to the increased glucose consumption by the bacterial cells and the inflammatory cells. The elevated lymphocyte count indicates the body's immune response to the infection. The ADA activity is increased due to the action of ADA on the bacterial nucleic acids.

**Why Each Wrong Option is Incorrect**
**Option A:** Elevated protein levels are a characteristic finding in TBM, so this option is incorrect.
**Option B:** Decreased glucose levels are a common finding in TBM, making this option incorrect.
**Option C:** Increased ADA activity is a specific finding in TBM, so this option is incorrect.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the CSF findings in TBM can be modified by the use of corticosteroids, which can decrease the ADA activity and glucose levels. Therefore, a single abnormal CSF finding may not be sufficient to diagnose TBM, and a combination of clinical and laboratory findings should be considered.

**Correct Answer: C. Normal ADA activity.**