题目

  —Who has taken my pen away?    —__________. He was here a moment ago. A. It must be Li Ping           B. It is Li Ping take C. Li Ping is                  D. Li Ping must take 答案：A 解析: 本题是对情态动词的考查。句意表示肯定的推测用must，而it指问句中提到的who。  如果x=1是方程mx2-3x-4=0的解，则m的值是77．