What method should you utilize to add the elements of list$2$ onto the end of list$1?$

What method should you utilize to add the elements of list$2$ onto the end of list$1?$

list$2.$extend$($list$1)$

list$2.$append$($list$1)$

list$1.$append$($list$2)$

list$1.$extend$($list$2)$