6. According to the passage, which of the following is (are) true of the ice ages?
I. The last ice age occurred about 25,000 years ago.
II. Ice ages have lasted about 10,000 years for at least the last several hundred thousand years.
III. Ice ages have occurred about every 100,000 years*6 for at least the last several hundred thousand years.
(A) I only
(B) II only
(C) III only
(D) I and only（C）
(E) I, II and III
7. It can be inferred from the passage that calcium carbonate shells信息题（有定位）
(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）
(E) reflect the isotopic composition of the water at the time the shells were formed由海水决定（<——）
8. The purpose of the last paragraph（延伸性内容） of the passage is to（难题）
(A) offer a note of caution提出令人警戒的注意事项
(B) introduce new evidence
(C) present two recent discoveries
(D) summarize material in the preceding paragraphs（A）
(E) offer two explanations for a phenomenon从全文的布局看，不是提供解释
9. According to the passage, one advantage（地理连续性，时间连续性） 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地理连续性
(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（B）
(E) provides data that can be used to substantiate records concerning variations in the amount of sunlight received by the Earth
责任编辑：sealion1986
