下面这篇短文中共有10处语言错误，每句中最多有两处。错误涉及一个单词的增加、删除或修改。增加：在缺词处加一个漏词符号（∧），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：在错的词下划一横线，并在该词下面写出修改后的词。
注意: 1.每处错误及修改均仅限一词；
2.只允许修改10处，多者（从第11处起）不计分。
I believe that everyone in the world loves their mother. So am
I. My
mother is a ordinary teacher. She works hard at school, just as other
mothers do every day. In fact, she isn’t good health. She have been suffering
from arthritis(关节炎) for many years. In spite of this, she never stops
working or giving up hope. I still remember the day and when my mother
received a card of congratulations for Teacher’s Day from her director. The
card was read “Thank you for your hard works; Happy Teacher’s Day to
you!” At that moment, I was so moving that tears came to my eyes. I am
proud of my mother because she is my best teacher as good as my mother.
的半圆弧形光滑轨道开口向上固定在水平面上，其中，
为圆心，
在同一水平线上，
为竖直半径.质量分别为
、
的光滑小球被固定于长度恰为
推至
处.若无初速释放后杆球仅限于竖直轨道平面内运动，且不计其他阻力，则下列说法正确的是（ ）
统的重力势能减小