It's a python problem, why is (a)?

(HARD) Consider the following class definition class SomeList(list): def init self,iterable-[1 self.Ist = list (iterable) What is the output of the following? >>> s = SomeList ( [1,2] ) >>s.append ( 3) >>> print( len (s) ) . a) 1 b) 2 C)3 d)4