Sorting a preexisting sequence of n elements can be accomplished with the heapsort algorithm by: a. calling make_heap on the entire sequence and then calling pop_heap on the entire sequence n times. b. calling push_heap on the entire sequence n times and then calling pop_heap on the entire sequence n times. c. calling make_heap on the entire sequence and then calling sort_heap on the entire sequence. d. calling push_heap on the entire sequence n times and then calling sort_heap on the entire sequence.