Long ago ,there lived in Greece a learned man. He was so well known for his good knowledge of almost everything that lots of people from all over the country came to learn from him. The great man taught his students whole-heartedly and answered their questions with great patience. One day a student asked him, " My dear teacher, didn't you say you yourself have many ,many more questions about things than we do? But I think we students have far more than you." With a smile on his face, the teacher drew two circles ,one as large as a big cake, the other smaller. Then he said , "Of course, I have learned much more. But it's wrong to think that a teacher has fewer questions than his students. Now, look at these two circles. The inside of the bigger one is my knowledge of things, and the inside of the smaller one is yours. Out of the circles is what is still unknown to us. Since mine is larger, I have to use the longer line to draw the bigger circle. That means I have more opportunities to face what is still unknown. And that's why I myself have more questions than you do. The more you learn , the more questions you have. You will never learn enough ,you know." From the passage we can learn that  _  .
the more questions we have, the more knowledge we may get it's never too old to learn every one of us should try to be a learned man a teacher should have many questions