高中英语改错在下面这篇改错中Today I was having a PE lesson while I fell do

高中英语改错
在下面这篇改错中
Today I was having a PE lesson while I fell down 1.____
and hurt my foot.I was in greatly pain at that moment,2.____
but I tried to act as if nothing has happened until the 3.____
class was over.Though I had difficulty walk back to 4.____
my classroom,I still didn't tell anyone but even refused 5.____
the offer of help of my classmates.As result,the hurt 6.____
in my foot became worse.Now I know I'm wrong.We 7.____
can tell others our need for help and accept his help.8.____
Some day we can not help others in return.In this way,9.____
we can get along to each other happily and peacefully.10.____
为什么第1个空要将While改成When?
用While为什么不行呢?