"Prairie Restaurant" is a well-known old-fashioned restaurant on the prairie, but it has some unwritten "rules". If "Prairie Restaurant" sells both red mutton and mutton soup on a certain day, then it must also sell Roasted whole lamb; the restaurant never sells roasted whole lamb on Sunday; . people are familiar with these "rules" and are accustomed to it. In addition, we also know that only when selling red mutton lamb, boss Wang would go to "Prairie Restaurant". If the above conclusion is true, then which of the following must also be true? ['Sunday boss will not go to "Prairie Restaurant" to eat.', 'If "Prairie Restaurant" sells red mutton lamb on Sunday, then it must not sell mutton soup on that day.', '"Prairie Restaurant" does not sell mutton soup on Sunday.', '"Prairie Restaurant" does not sell red mutton only Sunday.']