Okay, let's tackle this question. The patient is a 60-year-old chronic smoker with hemoptysis and a normal chest X-ray. The next best investigation is being asked.

First, I need to recall the approach to hemoptysis. Hemoptysis can range from mild to massive, and the cause varies. Common causes include bronchitis, bronchiectasis, tuberculosis, lung cancer, and others. Since the chest X-ray is normal, it rules out some obvious issues like pneumonia or large masses. But in a chronic smoker, lung cancer is a big concern, even if the X-ray is normal. However, a normal X-ray doesn't rule out lung cancer entirely.

The next step after a normal chest X-ray in someone with hemoptysis, especially a smoker, would typically be a CT scan. A CT chest provides more detailed images and can detect smaller lesions, nodules, or abnormalities that an X-ray might miss. So CT is the next best investigation here.

Now looking at the options, the correct answer should be CT scan. Let me check the options again. The user didn't list the options, but assuming the options include CT scan. The other options might be sputum culture, bronchoscopy, or maybe another imaging modality. Sputum culture is useful for infections like TB, but if the X-ray is normal, maybe the issue isn't infectious. Bronchoscopy is invasive and might be considered if CT shows something suspicious. So CT is the logical next step.

Wait, but sometimes bronchoscopy can be the next step if there's a high suspicion of cancer despite normal X-ray. However, bronchoscopy is more direct but less sensitive than CT. So in the absence of a CT, bronchoscopy might be done, but CT is the preferred initial step because it's non-invasive and can guide further steps.

So the correct answer is CT chest. The other options are less appropriate. Sputum tests might miss cancer, and bronchoscopy is more invasive. So the next best investigation is CT scan.

**Core Concept**
Hemoptysis in a chronic smoker with a normal chest X-ray requires high-resolution imaging to detect occult lung pathology. **CT chest** is superior to X-ray for identifying small nodules, bronchiectasis, or early-stage lung cancer.

**Why the Correct Answer is Right**
A **CT scan of the chest with contrast** provides detailed cross-sectional imaging, detecting abnormalities like endobronchial tumors, peripheral lung lesions, or subtle infiltrates missed on X-ray. In smokers, this is critical for early lung cancer detection, as 80–90% of cases are nonsmall cell lung cancer (NSCLC), often presenting with hemoptysis and normal X-rays.

**Why Each Wrong Option is Incorrect**
**Option A:** *Sputum cytology* is low yield for occult cancer and lacks sensitivity for early-stage disease.
**Option B:** *Bronchoscopy* is invasive and reserved for CT-detected lesions or when CT is contraindicated.
**Option C:** *Pulmonary function tests* assess airflow obstruction but do not identify the cause of hemoptysis.

**Clinical Pearl / High-Yield Fact**
Never skip **CT chest** after a normal X-ray in hemoptysis, especially in high-risk patients (e.g., smokers).

✓ Correct Answer: A. Bronchoscopy