Question $21$

What will this mystery form do$?$

$($define mystery Clambda $($x$)($if $($null$?($cdr $x))$

$O$

$($append $($list $($car x$))($mystery cdr $x))$

$($mystery$\text{'}\text{'}(12$

Nothing! All it does is reassemble the list in order

It will reverse the list

It will do a reverse $($cdr $...),$ returning the front of the list as a list without the last element.

It will create a list with every other element of the passed in list