内壁光滑的环形凹槽半径为R，固定在竖直平面内，一根长度为 $\sqrt{2}$ R的轻杆，一端固定有质量m的小球甲，另一端固定有质量为2m的小球乙．现将两小球放入凹槽内，初始时刻小球乙位于凹槽的最低点（如图所示），由静止释放后（   ）

已知A，B是球O的球面上两点，∠AOB=90°，C为该球面上的动点，若三棱锥O﹣ABC体积的最大值为36，则球O的表面积为（　　）

    He's an old cobbler(修鞋匠) with a shop in the Marais, a historic area in Paris. When I took him my shoes, he at first told me: “I haven't time. Take them to the other fellow on the main street; he'll fix them for you right away.”

    But I'd had my eye on his shop for a long time. Just looking at his bench loaded with tools and pieces of leather, I knew he was a skilled craftsman(手艺人). “No,” I replied, “the other fellow can't do it well.”

    “The other fellow” was one of those shopkeepers who fix shoes and make keys “while-U-wait” — without knowing much about mending shoes or making keys. They work carelessly, and when they have finished sewing back a sandal strap(鞋带), you might as well just throw away the pair.

    My man saw I wouldn't give in, and he smiled. He looked at my shoes, had me write my name on one shoe with a piece of chalk and said, “Come back in a week.”

    I was about to leave when he took a pair of soft leather boots off a shelf.

    “See what I can do?” he said with pride. “Only three of us in Paris can do this kind of work.”

    When I got back out into the street, the world seemed brand-new to me. He was something out of an ancient legend, this old craftsman with his way of speaking familiarly, his very strange, dusty felt hat, his funny accent from who-knows-where and, above all, his pride in his craft.

    These are times when nothing is important but the bottom line, when you can do things any old way as long as it “pays”, when, in short, people look on work as a path to ever-increasing consumption(消费) rather than a way to realize their own abilities. In such a period it is a rare comfort to find a cobbler who gets his greatest satisfaction from pride in a job well done.

故乡（节选）

    我这时很兴奋，但不知道怎么说才好，只是说：“阿！闰土哥，——你来了？……”

    我接着便有许多话，想要连珠一般涌出：角鸡，跳鱼儿，贝壳，猹……但又总觉得被什么挡着似的，单在脑里面回旋，吐不出口外去。

    他站住了，脸上现出欢喜和凄凉的神情；动着嘴唇，却没有作声。他的态度终于恭敬起来了，分明的叫道：“老爷！……”

    我似乎打了一个寒噤；我就知道，我们之间已经隔了一层可悲的厚障壁了。我也说不出话。

    他回过头去说，“水生，给老爷磕头。”便拖出躲在背后的孩子来，这正是一个廿年前的闰土，只是黄瘦些，颈子上没有银圈罢了。“这是第五个孩子，没有见过世面，躲躲闪闪……”

    母亲和宏儿下楼来了，他们大约也听到了声音。

    “老太太。信是早收到了。我实在喜欢的了不得，知道老爷回来……”闰土说。

    “阿，你怎的这样客气起来。你们先前不是哥弟称呼么？还是照旧：迅哥儿。”母亲高兴的说。

    “阿呀，老太太真是……这成什么规矩。那时是孩子，不懂事……”闰土说着，又叫水生上来打拱，那孩子却害羞，紧紧的只贴在他背后。

    “他就是水生？第五个？都是生人，怕生也难怪的；还是宏儿和他去走走。”母亲说。

    宏儿听得这话，便来招水生，水生却松松爽爽同他一路出去了。母亲叫闰土坐，他迟疑了一回，终于就了坐，将长烟管靠在桌旁。