See program bubblesort.cpp$.$ This program contains three different versions of the bubble sort algorithm. It is known that the average run$-$time complexity of this algorithm is quadratic. Which of the three versions has a best case run$-$time complexity that is linear?

Version $2,$ bubblesort$2,$ is linear in the best case.

Version $3,$ bubblesort$3,$ is linear in the best case.

Both versions $2$ and $3$ are linear in the best case.

None of these have a best case run$-$time that is different from quadratic.