阅读下面短文，掌握其大意，然后根据所给单词的适当形式填空，使短文内容通顺、合理。并将答案完整的填在答题卷上。

In England, people often talk about the weather. Maybe they can experience (经历) four s___1___ in one day. In the morning the weather is warm just like in spring. An hour l___2___ black clouds come and then it rains h___3___. The weather gets a little cold. In the late afternoon the sky will be s___4___, the sun will begin to s___5__, and it will be summer at this time of a day.

In England, people can a__6___ have summer in winter, or have winter in summer. So in winter they can s___7___ in the sea sometimes, and in summer sometimes they should take warm clothes.

When you go to England, you will see that some English people usually take an umbrella or a raincoat w___8_ them in the sunny morning, but you should not l___9___ at them. If you d___10___ take an umbrella or a raincoat, you will regret (后悔) later in the day.

(18分）如图所示，一个圆弧形光滑细圆管轨道ABC，放置在竖直平面内．轨道半径为R，在A点与水半地面AD相接，地面与圆心O等高，MN是放在水平地面上长为3R，厚度不计的垫子，左端M正好位于A点将一个质量为m、直径略小于圆管直径的小球从A处管口正上方某处由静止释放，不考虑空气阻力。

（1）若小球从C点射出后恰好能打到垫子的M端，则小球经过C点时对管的作用力大小和方向如何？

（2）欲使小球能通过C点落到垫子上，小球离A点的高度H应是多少？