根据短文内容选择正确答案。
Today I went to Sam's school in the UK. It was really different from my school in China.
Girls wore grey skirts and white shirts, boys wore grey trousers, and everyone wore the school tie.
Some of Sam's lessons were a bit strange for me. We were reading Shakespeare in the English lesson, and there were quite some old words like "thou" and "thee" to mean "you". In history we studied 20th Century China. It was strange hearing a foreign side of history — and hearing English people trying to say all our Chinese names!
Classes were also a lot more relaxing than in China. Teachers were called "sir" or "miss", everyone shouted answers and raised their hands in classes. It was more like a debate than a class. A bell rang at the end of each lesson and everyone jumped up to go to the next class.
At break we bought potato chips and cookies in the dining room. Lunch was later than in China at 1 o'clock. We had big plates of pie with carrots. For dessert there was hot sweet rice called rice pudding.
It was good that I'd had an excellent lunch, because at Sam's school Monday afternoons are taken up with sports.
I played my first game of netball — a bit like basketball, but with some differences. Luckily I'd had a quick look in the rule book before I tried to join in the game.
，下列命题中不正确的是( )
的轻杆下端固定一个质量为
的小球，上端连在光滑水平轴上，轻杆可绕水平轴在竖直平面内运动（不计空气阻力）．当小球在最低点时给它一个水平初速度
，小球刚好能做完整的圆周运动．若小球在最低点的初速度从