Iterations of Apriori Algorithm terminate after finding only one $4-$item frequent itemset as $\{$P$,$ Q$,$ R$,$ S$\},$ where $\{$P$\},\{$Q$\},\{$R$\}$ and $\{$S$\}$ are few $1-$item itemsets. What is true about all the frequent itemsets for the involved transactions?

Group of answer choices

Minimum of $16$ frequent itemsets, but exact count is indeterminate.

Minimum of $15$ frequent itemsets, but exact count is indeterminate.

Exactly $16$ frequent itemsets

Maximum of $15$ Closed frequent itemsets