A trend away from stable, relatively high humidity in the Middle East over the past 8 million years can be inferred from the composition of cave formations dating to different periods. Cave formations from about 7 million years ago mainly consist of transparent columnar calcite, indicative of an underground water system regularly replenished by rainfall. Cave formations younger than approximately 1 million years, however, mainly consist of branching, opaque (and sometimes colorful) material, often with more frequent growth interruptions, indicating an intermittent water supply.
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Verbal·Craft and Structure·Text Structure and Purpose
hardWhich choice best describes the function of the two underlined portions in the text as a whole?
A
They describe divergent features of cave formations that when taken together imply decreasing variation in Middle Eastern rainfall over time.
B
They identify different characteristics of cave formations that when considered together provide evidence for a long-term shift toward lower and more variable humidity in the Middle East.
C
They provide evidence from different Middle Eastern cave formations that substantiates the claim that the region experienced a long period of relatively high humidity.
D
They draw a contrast between Middle Eastern cave formations that is suggestive of geographic differences in the underground water supply.