A、They were produced by British chain store. B、They were genetically engineered food . C、Tesco was itself fooled by the provider

Most people know that April 1" is called April Fool’s Day because people often play practical jokes on each other on this day. However, it’s not just friends and family you have to be ware of—big companies, newspapers and TV stations also do their best to fool the public.
    In 2002.the British supermarket chain, Tesco.advertised a "whistling carrot".(27)The ad explained that the carrot had been genetically engineered to grow with air holes down the side so that it would start whistling when it was fully cooked.
    This advert is relatively recent, whereas Britain’s most famous April Fool hoax is much older.
    Another famous April Fool’s Day joke comes from 1962. Sweden. It was announced on the news that it had become possible to watch colour programmes on black and white TVs because of some new technology the TV station had invented.(28)People were told to pull a nylon stocking over the screen so they would be able to watch the programmes in colour. Since almost everyone in Sweden had a black and white TV in those days, hundreds of thousands of people tried to do this, even though the news was broadcast on the morning of April 1st.
    You might think that people were more easily fooled back in those days. Nevertheless, you should be careful next April 1st—this time the April Fool might be you!
26. Q: What do people usually do on April 1?
27. Q: What do we know about the "whistling carrot"?
28. Q: According to the TV station in Sweden, what should people do to watch color programs?