A、He studied the designs of various clocks. B、He did experiments on different materials. C、He bought an alarm clock with a pig f

When Matty Sallin was working on a degree in arts and technology at university, he got an interesting assignment in electronics class: create something for the household. He decided to create an alarm clock. "Everybody has to use an alarm clock of some kind every day, and it’s extremely unpleasant!" he says. He asked different people what they’d like to wake up to instead of a noisy alarm. A lot of them said "the smell of bacon." So Sallin invented a new kind of alarm clock: a wooden box with a pig face and a digital clock that uses the smell of cooking bacon rather than sound to wake someone up. He explains, "There’s no danger of burning, because I built it carefully. It uses light bulbs instead of a flame for cooking and turns off automatically after ten minutes."Just a few easy steps are required to set the "alarm." "What you do is put in a couple of frozen strips the night before," says Sallin. Bacon is preserved, so there is no danger of its spoiling overnight. "If you set the alarm for 8:00, it will turn on at 7:50 and slow cook for ten minutes under the bulbs," he says. "Then the bulbs turn off and a fan blows the smell out through the nose of the pig. So instead of an alarm, you smell yourself awake," says Sallin. "Then you can open the door on the side and pull the bacon out and eat it."
Questions 20 to 22 are based on the passage you have just heard.
20. What was Matty Sallin doing when he created an alarm clock?
21. What did Matty Sallin do before making the new type of alarm clock?
22. What makes the newly invented alarm clock so unique?