关于力学单位制，下列说法正确的是（ ）
A．kg、m∕s、N是国际单位的导出单位
B．kg、m、s是国际单位的基本单位
C．在国际单位制中，质量的单位是kg．也可以是g
D．在国际单位制中，牛顿第二定律的表达式是F=ma
A、kg是国际单位中的基本单位，m/s、N是导出单位．故A错误．
B、kg、m、s是国际单位中的基本单位．故B正确．
C、在国际单位中，质量的单位是kg，g不是国际单位．故C错误．
D、在国际单位制中，1kg．m/s2=1N．所以F=ma．故D正确．
故选BD．
根据中文提示和英文书信内容，写一封意思连贯、符合逻辑、不少于60词的回信，信的开头和结尾已给出，其字数不计入所完成的回信内。 请不要写出你的姓名和学校。 假设你叫杨洋。是加拿大中学生Paula的笔友，下面是你收到的她的电子邮件。请你根据她来信的内容写一封回信。针对她的问题，谈谈你的看法，同时提出一些帮助她解决问题的建议。
I can understand your feeling. But I don’t think it is right for you to do things like that. Don’t worry. Here are some suggestions for you. As a student, it’s important for you to study hard to get more knowledge. So I think doing homework is necessary and useful. You should do your homework first. If it is not too late, you can play computer games for a while. Remember to go to bed as early as possible, then you won’t feel tired the next day. In class, you need to listen to the teachers carefully and take notes. What’s more, it’s important to take part in class activities, try to answer at least two questions each class. When you have any problems, ask your teachers or classmates for help. I ’m sure you’ll make great progress and pass the final exam. Good luck! Dear Paula: I’m sorry to hear you are in trouble now.___________________________________________ _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________I believe if you work hard you’ll make some progress. Good luck! yours Paula Dear Paula, Yours, Yang yang |
