@echo off
setlocal enabledelayedexpansion
for /f "tokens=1* delims=:" %%i in ('findstr /n .* a.txt') do set max=%%i
for /f "delims=" %%a in (b.txt) do call :couq&echo %%a!num!
pause
exit
:couq
set /a sui=%random%%%%max%+1
for /f "tokens=1* delims=:" %%i in ('findstr /n .* a.txt') do (
  if "%%i"==!sui! set num=%%j&goto :eof
)
goto :eof

setlocal enabledelayedexpansion
for /f "delims=" %%a in (A.txt) do (
   call :loop
   echo %%a!str_temp!>>C.txt
)

:loop
set /a rand_num=%random%%%5+1
set num=1
for /f "delims=" %%i in (B.txt) do (
   if !num!==%rand_num% (
    set str_temp=%%i 
    goto :eof
  )
   set /a num=!num!+1
)