The Earth's magnetic field is generated as the molten
iron of the Earth's outer core revolves around its solid
inner core; when surges in the molten iron occur, magnetic
tempests are created. At the Earth's surface, these tempests
can be detected by changes in the strength of the Earth's
magnetic field. For reasons not fully understood, the field
itself reverses periodically every million years or so.
Clearly, geophysicists who seek to explain and forecast
changes in the field must understand what happens in the
outer core. Unlike meteorologists, however, they cannot
rely on observations made in their own lifetimes. Whereas
atmospheric storms arise in a matter of hours and last for
days, magnetic tempests develop over decades and persist for
centuries.
7.In the passage, the author is primarily concerned with
(A) analyzing a complicated scientific phenomenon
and its impact on the Earth's surface features
(B) describing a natural phenomenon and the
challenges its study presents to researchers
(C) discussing a scientific field of research and the
gaps in researchers' methodological
approaches to it
(D) comparing two distinct fields of physical science
and the different research methods employed
in each
(E) proposing an explanation for a geophysical
phenomenon and an experiment that could help
confirm that explanation
研究者研究magnetic tempest的方法是detected by changes in the strength of the Earth's magnetic field,文章并没有或这个探测方法本身存在任何问题,仅仅是说,因为这个现象发展时间比较长,持续时间几个世纪,而研究者的寿命又比较短,因此不能在他的生命里完成这个工作(但不代表这个方法不能在下一个工作者那一代完成,方法学是没问题的),而C选项说的是方法学就有问题,完成不了的意思(我觉得gap就这个意思),比B过头多了,这对研究者来说,是一个challenge,但是对研究方法来说,不存在什么gap