Given the following array [5, 3, 6, 7, 15, 12, 16, 17, ?] and assuming that Quicksort will be used to sort this array in ascending order, select a value for the last element of the array (indicated by "?") such that the partitioning performed by Quicksort is most balanced.
a. 2
b. 18
c. 1
d. 9