如图甲所示，水平地面上的一物体，受到方向不变的水平推力F的作用，F的大小与时间t的关系和物体速度v与时间t的关系如图乙所示．则第2秒末时，物体处于____状态，第4秒末时物体受到的摩擦力为____N．第6秒末到第9秒末，推力F功率是____W．

    We'll have a Christmas Party on Christmas Day! What can you do for the party，my dear friends? Oh，let me see.Tina can sing some nice songs.Mary can dance.Peter can do some kung fu.Mike can draw cartoons.Liu Yun can play the pipa and John can play the piano.They are helpful! What can I do? Oh，I can play the violin! My English teacher，Miss Lee，can sing and dance for us.We are so happy and we can't wait!

唐代有一位书法家的作品千变万化，神采飘逸，极有情趣，被人称之为“变动如鬼神，不可端睨”“挥毫落纸如云烟”。下列作品最能体现其书法特点的是