Consider the incomplete Scala definition where some types have been replaced with question marks:

def f$($x: List$[$Int$],$ y: $?1)$ : $?2=$ x :: y

Which types must replace $?1$ and $?2$ for this definition to typecheck correctly?

Options:

$?1=$ Int and $?2=$ List$[$Int$]$

$?1=$ List$[$Int$]$ and $?2=$ List$[$Int$]$

$?1=$ Int and $?2=$ Int

$?1=$ List$[$List$[$Int$]]$ and $?2=$ List$[$List$[$Int$]]$

$?1=$ List$[$Int$]$ and $?2=$ List$[$List$[$Int$]]$