Which of the following is not a requirement of the combinations rule, subscript n baseline upper c subscript requalsstartfraction n exclamation mark over r exclamation mark left parenthesis n minus r right parenthesis exclamation mark endfraction , for items that are all different? choose the correct answer below. a. that r of the n items are selected (without replacement). b. that there be n different items available. c. that order is not taken into account (consider rearrangements of the same items to be the same). d. that order is taken into account (consider rearrangements of the same items to be different sequences).