A student of mine asked about the follwing sentence:
All you need to do is fill out the necessary information and bring it back to me.
She is wondering why she can't use the infinitive form "to fill out" in this sentence. My opinion is that "fill out the necessary information and bring it back to me" is functioning as a command within this sentence, in which case the infinitive would not be appropriate. Is that the best explanation, or is there a better one?