Section $6\mathrm{.}4\mathrm{.}3$ discusses an improved form of bubble sort, which it calls bubble sort $3.$ Although in the worst case bubble sort $3$ can require $($n $1)\backslash$times n $/2$ comparisons, the same as exchange sort, bubble sort $3$ has a particular feature that means it will generally take fewer comparisons. Explain what this feature is and describe what kind of data it makes bubble sort $3$ useful for sorting.