Perhaps their rush to adulthood is driven by a simple need to keep warm.
Located in tropical areas at low altitudes, savannas are stable ecosystems, some wet and some dry consisting of vast grasslands with scattered trees or shrubs.
规律41：挑选关键词的一个原则：具体，直接，生疏。比如上句中，不考虑状语修饰的问题，关键词为tropical, low altitude, savanna, wet, dry, grassland, scattered, shrubs。
They occur on a wide range of soil types and in extremes of climate.
规律42：表示“发生”类的词往往是比较虚的词，不需要特别记忆。如occur,happen, take place等。
Savannas typically experience a rather prolonged dry season.
规律43：有的时候，要学会分辨“无用”的概念。比如experience a xx season其实属于虽然具体，但无用的概念。我们可以直接把这句话理解为Savanna could be dry for a long period.
For example, savanna soils, like many rain forest soils, are typically oxisols (dominated by certain oxide minerals) and ultisols (soils containing no calcium carbonate), with a high acidity and notably low concentrations of such minerals as phosphorus, calcium, magnesium, and potassium, while aluminum levels are high.
These soils usually contain large amounts of clay and easily become water-saturated.
Sandy soils are prone to the leaching of nutrients and minerals and so tend to be nutritionally poor.
规律46：prone to do这类词可以和fail to do这类词做等同，都可以当做表示某种倾向的“情态动词”。
Evidence from other studies suggests that exclusion of fire results in markedly decreased plant-species richness, often with an increase in tree density.
On certain sites, particularly in South America, savanna formation seems related to frequent cutting and burning of moist forests for pastureland.
规律48：be related to 和be associated with 很多地方很相似，都可以表示多重逻辑。比如这里，related to偏向于因果。