9. Consider the following Python program y = 3; def subl(): a=7; def sub2 ): global x; a = 13; x 15; w17 def sub3 ) nonlocal a; a = 19; z23 List all the variables, along with the program units where they are declared, that are visible in the bodies of subl, sub2, and sub3, assum- ing static scoping is used