如图所示，物块放在水平面上，用与水平方向成30°角斜向上的拉力F拉物块时，物块能在水平面上作匀速直线运动，若F大小不变，而改用沿水平方向拉物块，物块仍能在水平地面作匀速直线运动，求物块与水平面间的动摩擦因数．

计算： $\sqrt[3]{64}$ － $\sqrt{81}$ ＋| $\sqrt{3}$ －2|－(1－ $\sqrt{3}$ ).

增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。

删除：把多余的词用斜线（＼）划掉。

修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1).每处错误及其修改均仅限一词。

2).只允许修改10处，多者（从第11处起）不计分。

Dear parents,

    The hardest time of my life is coming, and I know you are worry about my studies and my life. I can say nothing and thanks to you for the special occasion. Words failed me when I want to express my thanks to you for the care you showed me in the past few years. These days I have been studying hard and have performed to the best of my ability in the tests. I'll try your best to accomplish my assignment in the coming days.

    After the college entrance examination, I intend to helping you do some housework, that I have seldom done before. And I want to learn to cook in order to personal prepare a dinner for you both.

    My dear parents, everything is going well with me. do to relax!

    Love from,

    Your son