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  6 that ninety pe使分式无意义，a的取值是 [    ]A．0B．1C．﹣1D．±1