Mr. and Mrs. Martin live in New York. Mr. Martin is a doctor and his office is in New York. Mrs. Martin teaches music at a school in New York.     They have two sons. Their sons' names are Ted and Roy. Ted is twenty years old. He is now in Taiwan. He is studying Chinese. He went to Taiwan last month and is going to stay there for two years. Roy is thirteen years old. He goes to high school. He likes sports very much. He likes swimming best. He can swim faster than his father. He wants to be the best swimmer in his school. How many people are there in his family?   _  .
Three. Four. Five. Six.