Desert regions, even if they had an abundance of rain, could never be truly green. The most important contributing factor is that desert soil is either too porous or too impermeable to hold water. Any rainfall that does occur quickly runs off and is lost, adding the danger of flash floods in barren areas. In fact, the environment is so hostile that only the hardiest of plants can survive. Because of the soil, the temperatures are extreme-hot under the sun and cold at night, for the soil reflects heat rather than absorbs it. Furthermore, the plant life that sustains humidity in lusher regions is missing in the desert. Therefore, the air and soil remain dry and unlikely to change.

(from Susan S. Johnston et a1 : Keys to Composition)

Question: Give three reasons why we should have cars that consume less petrol.