Many people go to school for an education. They learn languages, history, politics, geography, physics, chemistry and mathematics. Others go to school to learn a skill so that they can make a living. School education is very important and useful. Yet, no one can learn everything from school. A teacher, no matter how much he knows, can not teach his students everything they want to know. The teacher's job is to show his students how to learn. He teaches them how to read and how to think. So, much more is to be learned outside school by the students themselves. It is always more important to know how to study by oneself than to memorize some facts or a formula . It is actually quite easy to learn a certain fact in history or a formula in math. But it is very difficult to use a formula in working out a math problem. Great scientists before us didn't get everything from school. Their teachers only showed them the way. Edison didn't even finish primary school. But they were all so successful. They invented so many things for mankind. The reason for their success is that they knew how to study. They read books that were not taught at school. They would ask many questions as they read. They did thousands of experiments. They worked hard all their lives, wasting not a single moment. Above all, they knew how to use their brain. According to the passage, the most important thing a teacher should do is   _  .
to teacher his students everything he knows to teach the students how to think to know everything they want to know to teach the students how to work out a math problem