What will be the output of the following Python code?

class Demo:
    def __init__(self):
        self.a = 1
        self.__b = 1
 
    def display(self):
        return self.__b
 
obj = Demo()
print(obj.__b)

A. The program has an error because there isn't any function to return self.a

B. The program has an error because b is private and display(self) is returning a private member

C. The program has an error because b is private and hence can't be printed

D. The program runs fine and 1 is printed

Answer: Option C