6. The APRIORI algorithm is being applied (with a user-specified support threshold) on a collection of transactions over the items {a,b,c,d,e,f}. Assume that the algorithm has identified the group of four-element frequent itemsets ( L4) consisting of: abcd, abce, abcf, acde, adef, bcde, and bcef. When the algorithm continues, how many initial candidate 5-itemsets are created and how many of them survive subset pruning (thus are ready for the scan)? a. 3 candidate itemsets (of 5 elements) are generated, none of them survives pruning b. 3 candidate itemsets (of 5 elements) are generated, one of them survives pruning c. 4 candidate itemsets (of 5 elements) are generated, one of them survives pruning d. 4 candidate itemsets (of 5 elements) are generated, two of them survives pruning