题目

如图所示，用细线竖直悬挂一质量为M的杆，质量为m的小环套在杆上，它与杆间有摩擦，环由静止释放后沿杆下滑过程中加速度大小为a，则环下滑过程中细线对杆的拉力大小为（ ） A . Mg B . Mg+mg C . Mg+mg－ma D . Mg+mg+ma 答案：C短文改错假定英语课上老师要求同桌之间交换修改作文，请你修改你同桌写的以下作文。文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加、删除或修改。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：在错的词下画一横线，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。Last weekend we went mountain-climbing. Even the heavy rain can not stop us. We set off early and went along an extreme narrow road, all in high spirit. On either side of the road was green fields. We could hear the sound of the rain mixing with our laughter. At noon we reached to the top of the mountain, there we were amazed by the beauty of the scenes. After short rest, we started going down. It rained more harder. We were wet all over, and we still felt happy.