D

D is directly opposed to the evidence in the passage. The passage tells us that we have less decomposition in cold climates, which makes it MORE suitable, not less suitable as D says.

Why is A incorrect? And what is the evidence in the premise that makes C correct?

A is wrong because there's just nothing in the passage that supports this. C is right because the passage tells us that dating accuracy depends on the climate of the site. Therefore, if the climate has changed radically, we cannot date it as accurately.

Why is E wrong

There's no support for the idea that eggshell itself survives better in the cold than in warm climates. The passage tells us that amino acids within eggshells decay slower in the cold, but this doesn't tell us about the rate of decay of the eggshell as a whole, or about their relative commonness at the time of their initial deposition.