题目

完形填空      阅读下面短文，从短文后所给的四个选项中，选出可以填入空白处的最佳选项。 Last month we asked our students  1    their free time activities. Our questions were about exercise , use of the Internet and watching TV . Here  2    the results. We found that only fifteen percent of our students exercise   3 . Forty-five percent exercise four to six times a week .Twenty percent exercise only one to three times a week .And twenty percent do not exercise      4   .   We all know that many students often  5 , but we were  该图示意地震波传播速度在地球内部的变化。在地幔中传播速度随深度增加的变化为A．横波减小，纵波增加B．横波增加，纵波增加C．横波减小，纵波减小D．横波增加，纵波减小