Why?

Ok, so my grandson is three years old and has moved into the "why?" stage. If you ask him to pick up his toys, his response is "why?" I say "Time for bed." His response is ... you guessed it! "WHY??" Everything is "why?" now and it makes me crazy! I know it is just a phase and he will move on to something else soon. Still, I have to bite my tongue to keep from answering his "Why?" with a "Because I said so that's why!" I know that unless he asks the questions he will not learn the answers. It still drives me a little nuts after repeating the answer only worded differently a half dozen times. Maybe I will turn the tables on him and answer "Why not?" and see what his responses are. This could be very interesting.