GRE Reading Comprehension
Currently, there are two models of solar activity. The first supposes that the Sun's internal motions (caused by rotation and convection) interact with its large-scale magnetic field to produce a dynamo, a device in which mechanical energy is converted into the energy of a magnetic field. In short, the Sun's large-scale magnetic field is taken to be self-sustaining, so that the solar- activity cycle it drives would be maintained with little overall change for perhaps billions of years. The alternative explanation supposes that the Sun's large-scale magnetic field is a remnant of the field the Sun acquired when it formed, and is not sustained against decay. In this model, the solar mechanism dependent on the Sun's magnetic field runs down more quickly. Thus, the characteristics of the solar-activity cycle could be expected to change over a long period of time.
Which of the following statements about the two models of solar activity, as they are described in the passage, is accurate?
- A In both models cyclical solar activity is regarded as a long-lived feature of the Sun, persisting with little change over billions of years.
- B In both models the solar-activity cycle is hypothesized as being dependent on the large-scale solar magnetic field.
- C In one model the Sun's magnetic field is thought to play a role in causing solar activity, whereas in the other model it is not.
- D In one model solar activity is presumed to be unrelated to terrestrial phenomena, whereas in the other model solar activity is thought to have observable effects on the Earth.
- E In one model cycles of solar activity with period- icities longer than a few decades arc considered to be impossible, whereas in the other model such cycles are predicted.
Correct Answer: B