Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
Put in ' the' if the speaker and hearer probably know exactly which ( one / ones ). Put in a, an, the, - (=no article) if he doesn't.