We can’t answer every question they have about the flat earth model, but neither can they answer every question we have about the globe earth model. So when they’re bombarding you with questions that you don’t have answers to, give them a few of your own:
1) Why can we see the Big Dipper all year 'round? We shouldn’t be able to do that on a spinning ball unless all of the stars are spinning with us.
2) Do you know the formula for the supposed curvature of the earth and have you ever tested it?