Reading Comprehension
试题详情
文章：
| Line | A small number of the forest species of |
| lepidoptera (moths and butterflies, which exist as | |
| caterpillars during most of their life cycle) exhibit | |
| regularly recurring patterns of population growth | |
| (5) | and decline—such fluctuations in population are |
| known as population cycles. Although many different | |
| variables influence population levels, a regular pattern | |
| such as a population cycle seems to imply a | |
| dominant, driving force. Identification of that driving | |
| (10) | force, however, has proved surprisingly elusive |
| despite considerable research. The common | |
| approach of studying causes of population cycles by | |
| measuring the mortality caused by different agents, | |
| such as predatory birds or parasites, has been | |
| (15) | unproductive in the case of lepidoptera. Moreover, |
| population ecologists’ attempts to alter cycles by | |
| changing the caterpillars’ habitat and by reducing | |
| caterpillar populations have not succeeded. In short, | |
| the evidence implies that these insect populations, if | |
| (20) | not self-regulating, may at least be regulated by an |
| agent more intimately connected with the insect than | |
| are predatory birds or parasites. | |
| Recent work suggests that this agent may be a | |
| virus. For many years, viral disease had been reported | |
| (25) | in declining populations of caterpillars, but population |
| ecologists had usually considered viral disease to | |
| have contributed to the decline once it was underway | |
| rather than to have initiated it. The recent work has | |
| been made possible by new techniques of molecular | |
| (30) | biology that allow viral DNA to be detected at low |
| concentrations in the environment. Nuclear | |
| polyhedrosis viruses are hypothesized to be the | |
| driving force behind population cycles in lepidoptera | |
| in part because the viruses themselves follow an | |
| (35) | infectious cycle in which, if protected from direct |
| sun light, they may remain virulent for many years | |
| in the environment, embedded in durable crystals of | |
| polyhedrin protein. Once ingested by a caterpillar, | |
| the crystals dissolve, releasing the virus to infect | |
| (40) | the insect’s cells. Late in the course of the infection, |
| millions of new virus particles are formed and | |
| enclosed in polyhedrin crystals. These crystals | |
| reenter the environment after the insect dies and | |
| decomposes, thus becoming available to infect | |
| (45) | other caterpillars. |
| One of the attractions of this hypothesis is its broad | |
| applicability. Remarkably, despite significant differences | |
| in habitat and behavior, many species of lepidoptera | |
| have population cycles of similar length, between eight | |
| (50) | and eleven years. Nuclear polyhedrosis viral infection is |
| one factor these disparate species share. |
题目：
The primary purpose of the passage is to
选项:
A、describe the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera
B、present evidence that refutes a particular theory about the driving force behind population cycles in lepidoptera
C、present a hypothesis about the driving force behind population cycles in lepidoptera
D、describe the fluctuating patterns of population cycles in lepidoptera
E、question the idea that a single driving force is behind population cycles in lepidoptera
答案:
C
还没有人问到这里，扫码去GMAT出国考试答疑器提问吧。
