A 35 year old male, with pre-morbid anxious traits and heavy smoker, believes that he has been suffering from 'lung carcinoma' for a year, No significant clinical finding is detected on examination and relevant investigation.He continues to stick to his belief despite evidence to the contrary.In the process, he has spent a huge amount of money, time and energy is getting himself unduly investigated.He is most likely suffering from -

• A. Delusional disorder
• B. Malingering
• C. Carcinoma lung
• D. Hypochondrical disorder