So long as you have put a great deal of effort， you can grind an iron rod into a needle-This legend is about Li Bai， a great poet in Tang Dynasty. Li Bai was naughty and disliked study when he was a child. One day he saw an old woman grinding an iron rod on a big stone when he was playing by a river. Driven by curiosity， Li Bai came up and asked，"What are you doing， granny?""Grinding an iron rod，" said the old women without stopping grinding."Then what for?" he asked again."To make a sewing needle，" was the answer."What?!" little Li Bai was puzzled， "You want to grind so big a rod into a needle? It will take many years.""This doesn't matter. As long as I persevere1 in doing so， there is nothing you cannot achieve in the world. Certainly I can make a needle from the rod."Deeply moved by what the old woman said， Li Bai took effort to study since then and finally became one of the greatest poets in China.