Over2,200yearsago,Chengduwasthreatenedbyfrequentfloods....
問題詳情：Over2,200yearsago,Chengduwasthreatenedbyfrequentfloods.LiBing,togetherwithhisson,decidedtoconstructanirrigationsystemontheMinjiangRiver____41____ (prevent)flooding. ___42___havingalongstudya...