短文改错。

    Jim Green teaches our ____ English. He has been in China for more than two year____. He has been to many interesting places in Beijing, and____  he has not yet been to many others ____ parts of China. Last week he goes ____ to Mount Emei in Sichuan Province with his family. Many people like travel ____ by air, but Jim ____ family think that traveling by train is the best. It is much cheap ____ and far more enjoyable than a rushing trip by air. He ____ had a wonderful train ride to Chengdu after ____ they went to Mount Emei by bus.

每周一的学校升旗仪式上，同学们都会高唱国歌。那么，谱写国歌的曲作者是谁？（    ）

假设雨点下落过程中受到空气的阻力与雨点(可看成球形)的横截面积s成正比，与下落速度_v的平方成正比，即f_阻=ksv²，其中k为比例常数。已知球的体积公式：$v=\frac{4}{3}\pi r^3$ (r为半径)，每个雨点的密度相同，且最终都做匀速运动。如果两个雨滴的半径之比为1∶4则这两个雨点的落地速度之比为(      )