甲班学生做完实验室制备氧气和还原金属氧化物的实验后，剩余物质倒入同一废液缸里．乙班课外兴趣小组同学进行了如图所示的探究．请回答：

一根轻质弹簧，竖直悬挂，原长为10 cm.当弹簧下端挂2.0 N的重物时，伸长1.0 cm；则当弹簧下端挂8.0 N的重物时，弹簧的长度为(     )

圈出句子中的错别字，并改正

①鲸的寿命很常，一班可以活几十年到一百年。    

②其实还有比象大得多的动物，那就是鲸。 

③目前以知最大的鲸约有十六万公斤重。      

如图所示，半径R=0.9m的光滑的半圆轨道固定在竖直平面内，直径AC竖直，下端A与光滑的水平轨道相切．一个质量m=1kg的小球沿水平轨道从A端以V_A=3 $\sqrt{5}$ m/s的速度进入竖直圆轨道，后小球恰好能通过最高点C．不计空气阻力，g取10m/s²．求：

根据短文理解, 从A、B、C三个选项中选择最佳答案填空。

    Are you ready for the adventure of your lifetime? Do you love to travel and 1 new people?

    If your answer 2 these questions is "Yes", then read on.

    Have you ever lived and studied in 3 country? No? Well, now it is your chance!

    Student exchange(交换) is fun, exciting and will teach 4 new things. It gives you the chance to experience a 5 culture and learn a new language. You will never have another experience like this!

    There are two stages(阶段) in every student exchange, a hosting stage and a visiting stage. For hosting stage, an exchange student will travel to your hometown and 6 with your family for three months. Then, you will travel to the hometown of your exchange partner and live with his or her family for three months 7 the visiting stage. You will go to school there and live just like a member of the host family.

    8 can go on a student exchange? All secondary school students can go on an exchange if you have done 9 in your class this year. You should be 14--17, and you would like to learn the language, culture, history, geography and the way of life in another country. And you should have your application (申请) approved (批准) by the head teacher.

    So, what are you 10 for? Apply today!