It is very likely that the part previous to this passage is about ______.

A．The climate in recorded human history has generally remained stable.
B．The climate from about 135,000 to 115,000 years ago was in a extremely cold state.
C．The human race has been lucky to have enjoyed the most favorable period of climate for them to build a socio-economic system.
D．The evidences scientists collected from the ice cores suggest that a civilization can not have arisen in the period from about 135,000 to 115,000.

A．there is an unseen hand controlling the earth' s movement
B．there is an operating manual warning people against air-conditioning in the factory
C．people should prepare operating manuals to tell workers how to get greater comfort
D．people have been enjoying the most comfortable climate in Earth' s history.