____÷2＝____，表示____里面有____个____。

   Dictionaries say that “spring fever” is a lazy or restless feeling . People usually have the feeling on the first warm day of spring. Everyone has probably felt it at one time or another . people have talked about it for years.
   Recently, scientists have taken a good look at spring fever. What they found is quite surprising.
   In many places we live in , the winter months often seem dark and dreary. When spring comes late March , the world becomes colorful . The number of daylight hours grows with each passing day. According to many scientists, all the sunlight sets off chemicals in the brain (大脑). The chemicals make our feeling change and bring on spring fever.

对于煤、石油、天然气叙述正确的是（　　）