**Core Concept**
The investigation of choice for Chronic Hypersensitivity Pneumonitis Syndrome (CHPS) involves assessing the immune system's response to inhaled antigens, which typically involves the identification of specific antibodies or antigens in the lungs.

**Why the Correct Answer is Right**
The investigation of choice for CHPS is High-Resolution Computed Tomography (HRCT) of the chest, which provides detailed images of the lung parenchyma and is essential for diagnosing and monitoring the progression of the disease. Additionally, HRCT can help identify specific patterns of lung injury associated with CHPS, such as ground-glass opacification and fibrosis. HRCT is non-invasive and can be repeated as needed to monitor treatment response.

**Why Each Wrong Option is Incorrect**
**Option A:** Blood tests, such as complete blood count (CBC) and liver function tests (LFTs), may be ordered to evaluate for systemic symptoms and potential liver involvement, but are not the investigation of choice for CHPS.
**Option B:** Pulmonary function tests (PFTs) can provide information on lung function and may show abnormalities in patients with CHPS, but are not specific or sensitive enough to diagnose CHPS.
**Option C:** Bronchoscopy with bronchoalveolar lavage (BAL) can be used to obtain samples for histological examination and may be helpful in diagnosing CHPS, but is not the primary investigation of choice.

**Clinical Pearl / High-Yield Fact**
CHPS is a complex disease that requires a comprehensive diagnostic approach, including HRCT, serological testing, and clinical correlation. It's essential to consider CHPS in the differential diagnosis of patients with chronic respiratory symptoms and abnormal HRCT findings.

**Correct Answer:** C.