题目

Mr. Smith thinks running is ________ than swimming. A. very popular           B. the most popular       C. more popular               答案：C用钢笔写字时，笔尖和纸面的摩擦是________，电脑上使用的鼠标下面有一个球形的轮子，在使用过程中与鼠标垫之间的摩擦是________．