Definition: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: Senior citizens are permitted to travel cheaply on a bus if they have a special card. Women may get cards when they are sixty. Mrs. Matthews lived in the country but she went into town once a week to buy food and other things for the house, and she usually went by bus. She always had to pay the full price for her ride. Then she reached the age of sixty and got her senior citizen's card, but when she used it for the first time on the bus, it made her feel very old. The bus driver had often seen her traveling on the bus before, and he noticed that she was feeling unhappy, so after she had paid her money, he winked at her and whispered, "Don't forget to give your mother's card back to her when you see her again." Mrs. Matthews was very happy when she heard this.
Answer: old people with special cards
Output:
Senior citizens in the story refer to _ .