Over2,200yearsago,Chengduwasthreatenedbyfrequentfloods....
问题详情：Over2,200yearsago,Chengduwasthreatenedbyfrequentfloods.LiBing,togetherwithhisson,decidedtoconstructanirrigationsystemontheMinjiangRiver____41____ (prevent)flooding. ___42___havingalongstudya...