A

　　Millions of people around the world cook their food over a smoky fire every day.It is often difficult to find wood for the fire.People who do not have wood must spend large amounts of money on cooking fuel.However，there is a much easier way to cook food using energy from the sun.

　　Solar cookers，or ovens，have been used for centuries.A Swiss scientist made the first solar oven in 1767.Today，people are using solar cookers in many countries around the world.People use solar ovens to cook food and to heat drinking water to kill bacteria and other harmful organisms.

　　There are three kinds of solar ovens.The first is a box cooker.It is designed with a special wall that shines or reflects sunlight into the box.Heat gets trapped under a piece of glass or plastic covering the top of the cooker.A box oven is effective for slow cooking of large amounts of food.

　　The second kind of solar oven is a panel cooker.It includes several flat walls，or panels，that directly reflect the sun's light onto the food.The food is inside a separate container of plastic or glass that traps heat energy.People can build panel cookers with very few supplies quickly.They do not cost much.In Kenya，for example，panel cookers are being manufactured for just two dollars.

　　The third kind of solar oven is a parabolic(抛物线的) cooker.It has rounded walls that aim sunlight directly into the bottom of the oven.Food cooks quickly in parabolic ovens.However，these cookers are hard to make.They must be re­aimed often to follow the sun.Parabolic cookers can also cause burns and eye injuries if they are not used correctly.

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