**Core Concept**
Recurrent hemoptysis in a young patient can be due to various causes, including pulmonary tuberculosis, bronchiectasis, or pulmonary embolism. However, the absence of abnormal findings on chest X-ray necessitates further investigation to identify the underlying cause.

**Why the Correct Answer is Right**
In cases where chest X-ray is normal, a high-resolution computed tomography (HRCT) of the chest is the preferred next step. HRCT provides detailed images of the lung parenchyma, bronchi, and blood vessels, allowing for the detection of small abnormalities that may not be visible on a standard chest X-ray. This is particularly useful in diagnosing conditions such as bronchiectasis, pulmonary tuberculosis, or small pulmonary emboli.

**Why Each Wrong Option is Incorrect**
* **Option A:** ECG is not a suitable next investigation for recurrent hemoptysis, as it does not provide information about the lungs or pulmonary vasculature.
* **Option B:** Pulmonary function tests (PFTs) may be useful in assessing lung function, but they do not provide a direct diagnosis for the cause of hemoptysis.
* **Option C:** Bronchoscopy can be useful for diagnosing conditions such as bronchitis or foreign body aspiration, but it is not the next best investigation in this case, where the X-ray is normal.

**Clinical Pearl / High-Yield Fact**
HRCT of the chest is particularly useful in diagnosing small pulmonary emboli, which may not be visible on a standard chest X-ray. A high index of suspicion for pulmonary embolism should be maintained in young patients presenting with recurrent hemoptysis.

**Correct Answer: C. Bronchoscopy**