51. If A is the brother of B; B is the sister of C; and C is the father of D, how D is related to A?
52. If A + B means A is the brother of B; A - B means A is the sister of B and A x B means A is the father of B. Which of the following means that C is the son of M?
53. Introducing a boy, a girl said, "He is the son of the daughter of the father of my uncle." How is the boy related to the girl?