A 40 year old man presents to casualty with history of regular and heavy use of alcohol for ten years and morning drinking for one year. The last alcohol intake was three days back. There is no history of head injury or seizures. On examination, there is no icterus, sign of hepatic encephalopathy or focal neurological sign. The patient had coarse tremors, visual hallucinations and had disorientation to time. Which of the following is the best medicine to be prescribed for such a patient ?