The letter that Joel has written is being read by Adam, so 
OPTIONS:
- Joel is the editor.
- Adam is the editor.
Adam is the editor.

I had to buy a skirt if I wanted to wear my new jacket. The 
OPTIONS:
- skirt I had did not match.
- jacket I had did not match.
skirt I had did not match.

The insulin was administered by mouth instead of by needle, as the 
OPTIONS:
- mouth was an effective delivery method.
- needle was an effective delivery method.
mouth was an effective delivery method.