def a(x, y): print("I am from function a") return x(y) def b(z): z() def c(): #register the address of function c with the content below. Function c is not run until function c is called outside on line 9. print("I am from function c") print("I am from function b") return c #return must be placed at the end of the function def d(): print("I am from function d") a(b,d)()