Which of the following is a valid doctest?

Questions & AnswersCategory: Programming LanguageWhich of the following is a valid doctest?
Adam asked 2 years ago

Which of the following is a valid doctest?
a. 

def add(x, y):

    """Returns sum of two numbers.

    """

    >>> add(5, 6)

    13

    return x + y

b.

def add(x, y):
    return x + y

c.

def add(x, y):

    """Returns sum of two numbers.

    >>> add(5, 6)

    13

    """

    return x + y

d.

def add(x, y):

    """Returns sum of two numbers.

    add(5, 6)

    13

    """
    return x + y