题目

-How did Lucy hurt herself?    -She ____ a big tree because she was reading while walking.   A. walked over    B. walked into   C. fell into    D. ran over 答案：B一人用力把质量为1 kg的物体由静止向上提高1 m，使物体获得2 m/s的速度，则（    ） A.人对物体做的功为12 J                       B.合外力对物体做的功为2 JC.合外力对物体做的功为12 J                D.物体克服重力做功为10 J