7. It can be inferred from the passage that calcium carbonate shells

（A） are not as susceptible to deterioration as rocks

（B） are less common in sediments formed during an ice age

（C） are found only in areas that were once covered by land ice

（D） contain radioactive material that can be used to determine a sediment’s isotopic composition

（E） reflect the isotopic composition of the water at the time the shells were formed

8. The purpose of the last paragraph of the passage is to

（A） offer a note of caution

（B） introduce new evidence

（C） present two recent discoveries

（D） summarize material in the preceding paragraphs

（E） offer two explanations for a phenomenon

9. According to the passage， one advantage of studying the isotope record of ocean sediments is that it

（A） corresponds with the record of ice volume taken from rocks on land

（B） shows little variation in isotope ratios when samples are taken from different continental locations

（C） corresponds with predictions already made by climatologists and experts in other fields

（D） confirms the record of ice volume initially established by analyzing variations in volcanic emissions

（E） provides data that can be used to substantiate records concerning variations in the amount of sunlight received by the Earth

參考答案：DDBC BCEAB