Answer:
C
Explanation:
(C) Chest x-ray
In this case, the best investigation would be a chest x-ray. The symptoms of sudden left-sided chest pain, dyspnea, and diminished air entry over the left chest zone suggest a possible lung issue such as a pneumothorax (collapsed lung) or pleural effusion. A chest x-ray can help visualize the lungs and chest cavity to identify any abnormalities that may be causing the symptoms. Other investigations like ECG, troponin level, CT scan, and lung function tests may be considered based on the initial chest x-ray findings and clinical assessment.