Father's father and mother are my ____．

　　A．grandfather　　B．grandmother

　　C．grandparents D．grandparent

A lot of boys and girls in western（西方的）countries are wearing the same kind of clothes, and many of them have long hair, so it is often difficult to tell whether（是否）they are boys or girls.
One day, an old man went for a walk in a park in Washington, and when he was tired, he sat down in a chair. A young person was standing on the other side of the pool.
“Oh!” the old man said to the person sitting be side him on the chair. “Do you see that person with the glasses and long hair? Is it a boy or a girl?” “A girl.” said the neighbor（隔壁的人）. “She is my daughter.” “Oh!” the old man said quickly. “Please forgive me, I did not know that you were her mother.” “I’m not.” Said the other person, “I’m her father.”
【小题1】What did the old man see on the other side of the pool?

My father’s _____ is my grandfather.

A. sister             B. mother      C. brother       D. father