根据短文理解，选择正确答案。
Many people go to school for an education. They learn languages, history, 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; no matter how much the teacher knows, he cannot 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 study by oneself than to memorize some facts or a formula(公式).
It is actually quite easy to learn a certain fact in history or a formula in mathematics. But it is very difficult to use a formula in working out a maths problem. Great scientists, such as Einstein, Newton and Galileo didn't get everything from 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 worked hard all their lives, wasting not a single moment. They would ask many questions at what they read and they did thousands of experiments.
，∠A＝30°，则∠B等于（ ）
