—Where are the books about computers,please?

—They are ______．[ ]

A. on Shelf C    

B. in Shelf A      

C. at Shelf B

联合国是目前世界上____________________国际组织，成立于______年，宗旨为________________________________________________________________。它唯一有权采取行动的机构是_________。它有5个常任理事国__________________。联合国总部设在____________。