I completely agree with Victor �s idea.

 

I also agree with joy2bill.  I appreciate having an answer key and I am also a native speaker.  It just makes the process of correcting worksheets/tests go a whole lot faster in my opinion.

 

On the other hand, I am not in favor of making it mandatory to provide an answer key.  I do think it �s very nice to provide an answer key if you happen to have one for your worksheet (in the same document or in the comments section as already suggested).   But I understand, as some have already noted above, that not everyone includes them and that is okay too! :)