语法填空
阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。
One afternoon many years ago, I sat down on a chair in a park and watched a little boy, around 2 years old, ________ (run) freely on the grass as his mother watched from a short distance.The boy would fall to the grass, get up, and without looking back at his mother, run as fast as he could as if nothing ________ ( happen).
When kids fall down, they don't think of the fall as________failure. Instead, they consider ________as a learning experience.They try and try again________  they succeed.
I was also touched by the way he ran. With each attempt, he looked so ________ (confidence) and natural.He only wanted to run freely and to do it as well as he could.He was just being a child--- being himself completely at the moment.He never gave up.Each time he fell, he got up again by________, as if he knew that falling down was________ (simple) a part of life.
He was not looking for others' smiles, or worrying________whether someone was watching or not. ________he wanted was to run and to feel the experience of running fully and freely.I learned a lot from the experience.