What is the run time for adding an element at the tail of a linked list of size n$,$ assuming that you are not maintaining a tail reference? $($Choose the best$/$fastest category that fits.$)$

Group of answer choices

O$(1)$

O$($n$2)$

O$(2$n$)$

O$($n log n$)$

O$($log n$)$

O$($n$)$