4. Consider the following Python program: x = 1; Y 3i z=5; det sub1) y 9 z = 11; def sub2: global x a 13 x = 15; def sub3() nonlocal a a 19; b 21; z=23; List all the variables, along with the program units where they are declared, that are visible in the bodies of subl, sub2, and sub3, assuming static scoping is used