Given the following function: def reverse$\_$str$($st$,$ pos$=0)$: $"""$ Returns a new string that is the reverse of st When first called, the pos parameter must be zero $"""$ if pos $==$ len$($st$)$: return $""$ return reverse$\_$str$($st$,$ pos$+1)+$ st$[$pos$]$ If a user were to call the function like this reverse$\_$str$("$recursion$")$ What would be the value of pos in the first call? Group of answer choices