题目

下面关于质点的说法，正确的是（      ）A.研究和观察日食时，可以把太阳看成质点B.研究地球公转时，可以把地球看成质点C.研究地球自转时，可以把地球看成质点D.原子很小，可以把它看成质点 答案：B【试题分析】观察日食时，太阳大小不能忽略，A错误；由于地球公转半径比地球半径大104倍还多，所以B正确；而研究地球自转时，其大小起决定性作用，因此不能看作质点，C错误；原子虽小，但研究其结构时，原子是不能看作质点的，D错误.故本题正确答案为B.Fights at school have become an increasingly familiar sight for children. You should know what to do if you are in a fight, or see a fight at school. 1.You should try to get away if you can. If you know someone is coming up behind you to attack, turn toward the person with your hands up in front of your body and loudly say “stop” before walking away. 2. If the person doesn’t stop, cry for help by calling out the name of a teacher whose classroom is nearby.3. In some school districts, everyone involved in a fight can be punished, regardless of who started it.What should you do if you sec a fight? You mustn’t jump in to break up a fight or help a friend. If you get involved in a fight, you become exposed to injuries and punishment. 4. It’s a good choice to find an adult or call the police. Shout loudly to break up the fight or warn that an adult is coming.5. It only provides temporary relief for the attacker and causes more trouble. If you are concerned about fights at school, the best thing you can do is talk to an adult who will listen and take action.A. Violence never solves problems.B. You should support one aide for good reason.C. There’re a few ways for you to defend yourself.D. You can do something if a fight breaks out at school.E. Loud voice can usually make the attacker calm down.F. The attacker usually stops when you’re running fast.G. Fighting, even in self-defense, should always be the last choice.