Why won't my downloaded command line tools (version 10.12) show up in X-code 10?

I had to download command line tools 10.12, because my computer hardware is not advanced enough for MacOS Mojave that command line tools 10.14 requires. Why will the older version not show up in x-code 10? Is it because command line tool 10.12 was for version 9.x of x-code? Where can I get x-code 9.x?