When you implement a bubble sort algorithm, you write

a$.$ two loop structures that are placed at the same level of indentation in sequence: one to swap out$-$of$-$order pairs in a list and a second to go through the list repeatedly

b$.$ one fewer loop structure than there are elements in the array

c$.$ a loop that iterates over a list multiple times with a second loop that swaps out$-$of$-$order pairs nested inside it

d$.$ an outer loop that makes pair comparisons and an inner loop that controls the number of times you walk through the list being sorted