Let the data set of transactions consist of the sets {1,2,3,4,5}, {1,2,5}, {1,2,3}, {1,2,4}, {2,3,4}, {2,4,5}, {1,3}, and {3,4}. Suppose that the support threshold for a frequent itemset is 4 (i.e., an itemset has to appear at least 4 times in the transactions to be frequent), how many frequent itemsets can be found based on this data set? (Hint: please use APRIORI algorithm and start with all the 1-item itemsets)