(b) Given a query "best car auto insurance", for an information retrieval system, three documents' term frequencies and the idfs of the four words are given as follows. Using BM25 calculate the ranking result of the three documents. Assume KI=2,b=0.75, the average document length in the system is 1600 , and the lengths of the three documents are: 1000,1500 , and 1200 respectively