我在Python中创建了以下2D数组（列表列表）：#creatinga2darray(3rowsby7columns)andpopulatingitwithnumbersmatrix=[1,2,3,4,5,6,7],[8,9,10,11,12,13,14],[15,16,17,18,19,20,21]rows=len(matrix)#findingthemaxnumberofrowsinthematrix,inthiscase3columns=len(matrix[0])#findingthemaxnumberofcolumnsineachrow,7inthiscase我试图在数组中搜索特定元