|In the grammar tool for this assignment (and probably
later ones as well), if you try to adjoin some XP at an X' of the same
category (say, an AdvP at Adv'), the result is completely wrong. I have
not been able to fix this bug.
If necessary, the workaround is to give the adjunct phrase some other provisional category. For instance, you could represent an adverb like before as if it were a pronoun (that is, of category D). Adjoin the adjunct where it belongs. That way you will have the right structure. Then use the magnifying glass and the Alt key (or Command key on a Mac) to change the category of the adjunct's spine (here, from D to Adv).