I have a question on interpreting this point:

At least two compositions are performed either after F and before R, or after R and before F.

I think normally the LSAT is going for F-X-X-R or R-X-X-F (with min 2-X) but being extra cautious in doing this problem I also included a possibility of X-X-R-F-X-X and X-X-F-R-X-X since it doesn't indicate the two compositions must be the same nor must they be between them. Is this incorrect to interpret it this way? Is it safe to assume it will ways be referring to just the first set ups? (F-X-X-R)

How can we assume that answer choice B assumes an ice age period? I agree that: given we are in an ice age the concentration of oxygen 18 is increased but I switched my answer because that explicitness is not present and we know only in an ice age period it is increased otherwise it is in statis from the precipitation. I am thrown off here because the other answer choices make the distinction and this one doesn't.

Admin Note: Edited title. Please use the format: "PT#.S#.Q# - brief description of the question"