The best way of learning a language is using it .The best way of learning English is talking in English as much as possible. Sometimes you'll get your words mixed up ( 混合)and people will not understand you .Sometimes people will say things too quickly and you can't understand them. But if you keep your sense of humor (幽默感),you can always have a good laugh at the mistakes you make(你所犯的错误). Don't be unhappy if people seem to be laughing at your mistakes（错误）. It is better for people to laugh at your mistakes than to be angry with you. because they don't understand what you are saying .The most important thing for learning English is : “Don't be afraid of making mistakes because everyone makes mistakes. ”

否定了“两个凡是”的方针，作出把党和国家的工作重心转移到经济建设上来，实行改革开放伟大决策的会议是（    ）

一座铁路桥全长1200米，一列火车开过大桥需花费75秒；火车开过路旁电杆，只要花费15秒，那么火车全长是____ 米．