如图所示，固定在竖直平面内的光滑圆环的最高点有一个光滑的小孔质量为m的小球套在圆环上一根细线的下端系着小球，上端穿过小孔用手拉住现拉动细线，使小球沿圆环缓慢上移在移动过程中手对线的拉力F和轨道对小球的弹力N的大小变化情况是（   ）

背景材料：在大型青春励志生活类角色互换纪实节目 “变形计”之《少年少年》中，讲述了一个家住贵州山区的十四岁留守儿童——梁训：父母长期在外打工，他一个人独自生活。每天，他除了干农活外，还要上山砍柴、打水、喂猪和学习。可他从不怨天尤人，对生活和学习充满了热情。
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Dear friend,
     I am 1 American school girl. My name is Alice Green. I am twelve. I 2 two brothers. My brothers and I 3 all at school. We go to school 4 Monday 5 Friday. We 6 have classes on 7and Sunday. We don't go to school on weekends. My father and my mother are teachers. They say China is great. I like 8, and I can sing a lot of songs. My brother and I like baseball and basketball. 9do you like? Let's10friends. Please write soon.
Yours,
Alice Green