Try this:
@echo off
setlocal
:Input
set opt1=
set opt2=
set /p opt1=Do you want to extract audio from this clip (y/n)
if not defined opt1 goto :Invalid
if .%opt1% EQU . goto :Invalid
echo %opt1%|findstr /i /r /c:"y" /c:"n">nul||goto :Invalid
set /p opt2=Write subtitle file (y/n)
if not defined opt2 goto :Invalid
if .%opt1% EQU . goto :Invalid
echo %opt2%|findstr /i /r /c:"y" /c:"n">nul||goto :Invalid
if /i %opt1% EQU Y set opts=-x
if /i %opt2% EQU Y set opts=%opts% --write-sub
echo youtube-dl %opts% some link
goto :eof
:Invalid
Echo You have entered an invalid option. Please enter only y or n
goto :Input