Mom prepared to go shopping on the supermarket sale event day, but she forgot the specific date of the event, so she asked the following five people, and their answers were: Grandpa: It's a weekend. Grandma: It's a day on Tuesday, Thursday or Saturday Daddy: No, it's Monday. Son: It's Monday, Wednesday, Friday, or one of the Sundays. Daughter: It's Friday. If only one of these five people is right, the supermarket sale event may be:. ['Monday.', 'Wednesday.', 'Friday.', 'Saturday.']