A、They work by motion. B、They work by electricity. C、They work by rubbing the food. D、They work by sending short waves. A

Microwave cooking is probably the best cooking discovery since fire. In fact, it might be better than fire, since microwaves, instead of a flame or an electric element, cook the food.
    Microwaves are short radio waves, similar to heat and light waves. They work by motion. They cause the molecules in food to move, which produces heat in the food rather than in the oven, and the heat cooks the food. It’s similar to rubbing your hands together when they’re cold.
    There is a legend behind the use of microwaves for cooking.
    Percy Le Spencer was employed by the Raytheon Company during World War II. One day in 1942 he was working with magnetic materials, which produced microwaves. When he pulled a candy bar from his pocket, it was a melted mess. Although Spencer was working on scientific experiments, not trying to invent a new way of cooking, he realized that it was the microwaves that had melted the candy.
    Spencer knew that if microwaves melted candy, they would cook other foods as well. The Raytheon Company agreed, and in 1947 it introduced its first microwave ovens to the public.
    The first ovens were suspected of causing health problems, but the new models are safe when the when the factory’s instructions are followed. Microwave cooking now can be found in many homes all over the world.