When did the sparrows settle in the Liu family yard?Nobody can tell for sure.Maybe the day the family moved in,when Mrs.Liu moved a nest from inside the house to a tree in the yard.Maybe it was the day when she spanked her son and denied him dinner for shooting the birds with a sling.Or maybe it was the day when the Liu family planted the first seedling–the family planted hundreds of them every year.As the trees grew into a forest,the number of sparrows in it also increased exponentially.