11.ACD【解析】可把小球和滑块在水平方向的运动看作人船模型,设滑块在水平轨道上向右运动了x,由滑块和小球组成的系统在水平方向时动量守恒,可得M=二解得x=0.3m,A项正确,B项错误;根据水平方向动量守恒定律,小球相对于初始位置上升到最大高度时小球和滑块的速度均为零,由能量守恒定律可知小球相对于初始位置可以上升的最大高度为0.45m,C项正确;根据动量守恒定律,在小球上升到轨道高度时,滑块的速度为零,由系统的能量守恒定律可知小球相对于初始位置可以到达的最大高度为h=0.45m,与水平面的夹角满足cos0.8,设小球从最低位置上升到最高位置的过程中滑块在水平轨道上又向右运动了x,由滑块和小球系统在水平方向时动量守恒有Lcos a-x解得x=0.24m,小球从初始位置到第次到达最大高度的过程中,滑块在水平轨道上向右移动了x+x=0.3m+0.24m=0.54m,D项正确。

短文改错Ever since I was a child, I have been dreaming of travelling A China. One of my goal was to learnChinese. I decided to follow an one- week course for some basic skills in Shanghai. In general, I should have hadgoalgroup lessons, but I got 30 hours of privately lessons since I was the only beginner that week! This helped me soprivatemany. Have a teacher all to me improved my study a lotmuch Havingbut I still had a long way to go. Though thegrammar was quite easy, the pronounce was extremely hard. My teacher was a"master of tea", she hadpronunciationstudied the art of tea-making. So every day she bring a different kind of Chinese tea to me!who书面表达rought

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