The information of the global climate conditions in the past can be obtained(获得)through _________.
A.separating carbon dioxide from the air
B.examining the growth ringsof trees
C.comparing temperatures in different areas
D.studying the ice and air caught in each layer
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这是一道细节推断题。根据第三段“And the ice and air caught in each layer have begun to answer questions about the climates in the past.”可判断出对沉积在各层的雪和对空气的研究可知道过去气候的状况。