单项选择题
Extinction is a process that can depend on a variety of ecological, geographical, and physiological variables. These variables affect different species of organisms in different ways, and should, therefore, yield a random pattern of extinction. However, the fossil record shows that extinction occurs in a surprisingly definite pattern, with many species vanishing at the same time.
Which of the following, if true, forms the best basis for at lest a partial explanation of the patterned extinction revealed by the fossil record ？（）
A.Major episodes of extinction can result from widespread environmental disturbances that affect numerous different species.
B.Certain extinction episodes selectively affect organisms with particular sets of characteristics unique to their species.
C.Some species become extinct because of accumulated gradual changes in their local environments.
D.In geologically recent times, for which there is no fossil record, human intervention has changed the pattern of extinction.
E.Species that are widely dispersed are the least likely to become extinct.
相关考题
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单项选择题
Currently, the number of first-time admissions of individuals diagnosed as manic-depressives to hospitals in Great Britain exceeds by nine times the number of admissions of such patients to public and private hospitals in the United States, even though the population size of the United States is many times that of Great Britain. Which of the following, if true, would be most useful to an attempt to explain the situation described above ？（）
A．The term manic-depressive refers to a wider range of mentally ill patients in Great Britain than it does in the United States.
B．The admission rate in the United States includes those individuals who visit clinics for the first time as well as those who are admitted directly to hospitals.
C．A small percentage of patients diagnosed as manic-depressive in Great Britain are admitted to private nursing homes rather than hospitals.
D．The variety of training institutions in psychology in the United States is greater than in Great Britain, reflecting the variety of schools of psychology that have developed in the United States.
E．Seeking professional assistance for mental health problems no longer carries a social stigma in the United States, as it once did. -
单项选择题
A new ordinance passed by the Gorenton Council a year ago banned the sale of all nonrecyclable plastic packaging for food being sold in Gorenton. A substantial percentage of Gorenton’s plastic waste, however, is still composed of nonrecyclable plastic food packaging. Which of the following, if true, best contributes to reconciling the apparent discrepancy above ？（）
A．Fewer food products are packaged in nonrecyclable plasticstoday than were so packaged a year ago.
B．The new ordinance affects only plastic food packaging and not other products packaged in plastic, many of which are sold in Gorenton.
C．Grocery and other stores in nearby suburban areas patronized by many Gorenton residents are unaffected by the new ordinance.
D．Many food products formerly packaged in nonrecyclable plastics are now specially packaged in recyclable plastic before being shipped so that they can be sold in Gorenton.
E．The total amount of both Gorenton’s trash and its plastic waste grew considerably over the past year. -
单项选择题
A tree’s age can be determined by counting the annual growth rings in its trunk. Each ring represents one year, and the ring’s thickness reveals the relative amount of rainfall that year. Archaeologists successfully used annual rings to determine the relative ages of ancient tombs at Pazyryk. Each tomb was constructed from freshly cut logs, and the tombs’ builders were constrained by tradition to use only logs from trees growing in the sacred Pazyryk Valley. Which one of the following, if true, contributes most to an explanation of the archaeologists’ success in using annual rings to establish the relative ages of the tombs at the Pazyryk site ？（）
A．The Pazyryk tombs were all robbed during ancient times, but breakage of the tombs’ seals allowed the seepage of water, which soon froze permanently, thereby preserving the tombs’ remaining artifacts.
B．The Pazyryk Valley, surrounded by extremely high mountains, has a distinctive yearly pattern of rainfall, and so trees growing in the Pazyryk Valley have annual rings that are quite distinct from trees growing in nearby valleys.
C．Each log in the Pazyryk tombs has among its rings a distinctive sequence of twelve annual rings representing six drought years followed by three rainy years and three more drought years.
D．The archaeologists determined that the youngest tree used in any of the tombs was 90 years old and that the oldest tree was 450 years old.
E．All of the Pazyryk tombs contained cultural artifacts that can be dated to roughly 2300 years ago.
