which sentence if placed between sentences 2 and 3 would most improve the clarity of the paragraph?
1)The controversy over climate change is ongoing in the United States. 2) While nearly all sscientists accept climate change as a reality, a large percentage of citizena remain skeptical, despite the evidence from ice core samples. 3) The evidence these samples provide points to a consistently increasing level of carbon dioxide in the atmosphere.

a) For example, there have been many hot summers on recent record and writers appear milder than in previous years

b)These are samples of ice taken in Anartica, providing a snapshot of the earths atmospheric conditions for many thousands of years

c) Other citizens disagree with the scientists supporting climate change

D) the number of skeptical citizens is steadily diminishing now that ice core samples have been used to prove climate change is a reality

Sentence B elaborates on the samples. It gives the source of the samples and explains the kind of evidence they provide which was hinted at in sentence 2.

Sentence 3 flowing from sentence B elaborates on the evidence from the core samples referred to in sentence 2 and B.

One more thing, unlike D, sentence B does not repeat any information that we already know.

The complete sentence with B inserted reads thus:

1)The controversy over climate change is ongoing in the United States.

2) While nearly all scientists accept climate change as a reality, a large percentage of citizens remain skeptical, despite the evidence from ice core samples.

b)These are samples of ice taken in Anartica, providing a snapshot of the earths atmospheric conditions for many thousands of years

3) The evidence these samples provide points to a consistently increasing level of carbon dioxide in the atmosphere.

Cheers!