Here's a suggestion I used to give to students regarding this issue:
Write an answer in such a way that even if I had never read the question, I would know what had been asked. "You recycle" is indeed a complete sentence. But it does not connect to the issue of respecting creation, which is what was asked about in the question. If the answer had been, " One way in which we can respect creation is to recycle," I would think the question was either (1) List ways in which we can respect creation, or maybe (2) What does recycling accomplish?" (or something along those lines)
Once I saw the other 3 answers, all adressing "ways to respect creation", it would be obvious that the first question/option I'd thought of was in fact the question asked. So perhaps what this teacher is looking for is an answer that indicates the question asked. Have your child read his answer to himself and ask, "Does my reply make it clear what the question was?"