---

1	def a():
2	    print('a() starts')
3	    b()
4	    d()
5	    print('a() returns')
6	
7	def b():
8	    print('b() starts')
9	    c()
10	    print('b() returns')
11	
12	def c():
13	    print('c() starts')
14	    print('c() returns')
15	
16	def d():
17	    print('d() starts')
18	    print('d() returns')
19	
20	a()