GRE Reading Comprehension: ETS-GRE阅读ETS - 39MW_JT6OY531X407

Which one of the following can be inferred regarding the two proposals discussed in the passage? A. Since their introduction they have sharply divided the scientific community. B. Both were formulated in order to explain changes in the frequency of polarity reversal. C. Although no firm conclusions regarding them have yet been reached, both have been extensively investigated. D. They are not the only proposals scientists have put forward to explain the phenomenon of polarity reversal. E. Both were introduced some time ago and have since fallen into disfavor among geophysicists.