[Clarence] took his granddaughter [Ann] to the zoo, but [Ann]'s sister [April] could n't go with them because she had the flu.
('April', 'Clarence')
[Clarence] took his granddaughter [Ann] to the zoo, but [Ann]'s sister [April] could n't go with them because she had the flu.
[{('April', 'grandfather', 'Clarence'): [('April', 'sister', 'Ann'), ('Ann', 'grandfather', 'Clarence')]}]
['sister', 'grandfather']