第二部分 阅读理解（共20小题；每小题2.5分，满分50分）
A
As we all know, millions of people worldwide cook their food over 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 cooker, or ovens, have been used for centuries. A Swiss scientist made the first solar oven in seventeen sixty-seven. 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 quickly and with very few supplies. 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 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 re-aimed often to follow the sun. Parabolic cookers can also cause burns and eye injuries if they are not used correctly.
You can make solar ovens from boxes or heavy paper. They will not catch fire. Paper burns at two hundred thirty-two degrees Celsius. A solar cooker never gets that hot. Solar ovens cook food at low temperatures over long periods of time. This permits people to leave food to cook while they do other things.
21. If you have much food to cook, you’d better choose ______.
A. a box cooker B. a panel cooker C. a parabolic cooker D. a paper cooker
22. According to the passage we can conclude that ______.
A. a panel cooker is easy to make B. a box cooker is easy to make
C. a box cooker is the most effective oven D. a panel cooker is the cheapest oven of the three
23. What is the main purpose of the author in writing the passage?
A. To advertise the solar ovens.
B. To help readers to save cost on fuel.
C. To tell the readers how to make solar ovens.
D. To give the readers brief introduction of solar ovens.
