(A) would be right if it said the oldest archaeological sites that we can accurately date using the eggshell technique are in cooler regions.

Southern Africa could still have the oldest sites – they’d just need to be dated using different methods.

(B) would find support if the stimulus featured claims about how eggshells are necessary to obtain accurate dates or the only source of material that can be dated in this way.

The word unsuspected is key here. The stimulus tells us 1) we measure decomposition to obtain accurate dates, and 2) decomposition rates vary with climate. If there are large, unsuspected climatic fluctuations, there will be a difference between the actual rate of decomposition and the assumed rate of decomposition, resulting in potentially-inaccurate data.

The weakly-worded “less likely to yield accurate results” is nice as well. Much better than “will certainly yield wildly inaccurate results,” for example.

(D) is wrong because it assumes a linear rate of decomposition. 200,000 is indeed ⅕ of a million, but perhaps amino acid decomposition starts off fast and slows over time.

“No longer be suitable for examination by the technique” is a bit weird, too. The technique itself measures the proportion of decomposed material, so the parts that have decomposed are suitable for examination.

(E) just ventures off into fully unsupported nonsense. It’s a claim about where eggs are found, whereas the stimulus is about how we measure decomposing amino acids in the eggs we find, however many there are.