A chest physician performs bronchoscopy in the procedure room of the out patient department.To make the instrument safe for use in the next patient waiting outside,the most appropriate method to disinfect the endoscope is by:

• A. 2% gluteraldehyde for 20 min
• B. 70% alcohol for 5 min
• C. 1% sodium hypochlorite for 15 min
• D. 2% formaldehyde for 10 min