Available choices: -bill -skin -growth -sugar -fat -H 2 O -organ -muscle

You are presented with the quiz "What part of a bird's body is generally adapted to the kind of food that they eat?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "bird beaks are generally adapted for the food they eat" and "birds have a beak or a bill". So, what's the best answer to the question?
Answer:
bill