In this section you will read a passage which is followed by several questions
For the questions you are to choose the one best answer, (А), (В), (C), or (D),
to each question.
In some rural agricultural societies, the collection of available fuel such as firewood, dung cake, and agricultural waste can take 200 to 300 person-days per year. As well as being time consuming, the typical patterns of collection lead to deforestation, soil erosion, and ecological imbalances. In the future, experts predict that even if food supplies are adequate for rural populations, fuel supplies for domestic use may not be.
In the light of such considerations, a team in India has developed a solar oven for home use. The oven is cheaply constructed, easily operated, and extremely energy efficient. The device consists of an inner and outer metal box, a top cover, and two panes of plain glass. The inner box is painted black to absorb maximum solar radiation. The space between the two boxes is filled with an insulating material, such as rice husks, which are easily available and which, because of their high silicon content, neither attract insects nor rot easily. Other easily available materials for insulation are ground nutshells or coconut shells. An adjustable mirror mounted on one side of the oven box reflects the sunlight into the interior, boosting the temperatures by 15-30 degrees Celsius. This is most useful during the winter when the sun is lower. Inside the oven, a temperature between 80 and 120 degrees Celsius above ambient temperature can be maintained. This is sufficient to cook food gradually but surely. Trials have shown that all typical food dishes can be prepared in this solar device without loss of taste or nutrition.