2011年2月18日 星期五

RC_TN7Q22~25 難題解析


文章日期:2011-02-18 16:13
GWD7-Q22 to Q25:
Earth’s surface consists of rigid
plates that are constantly shifting and
jostling one another. Plate movements
Line are the surface expressions of motions



(5) in the mantle—the thick shell of rock
that lies between Earth’s crust and its
metallic core. Although the hot rock of
the mantle is a solid, under the tre-
mendous pressure of the crust and
(10) overlying rock of the mantle, it flows like
a viscous liquid. The mantle’s motions,
analogous to those in a pot of boiling
water, cool the mantle by carrying hot
material to the surface and returning
(15) cooler material to the depths. When
the edge of one plate bends under
another and its cooler material is con-
sumed in the mantle, volcanic activity
occurs as molten lava rises from the
(20) downgoing plate and erupts through the
overlying one.
Most volcanoes occur at plate
boundaries. However, certain “mis-
placed” volcanoes far from plate
(25) edges result from a second, indepen-
dent mechanism that cools the deep
interior of Earth. Because of its prox-
imity to Earth’s core, the rock at the
base of the mantle is much hotter than
(30) rock in the upper mantle. The hotter the
mantle rock is, the less it resists flow-
ing. Reservoirs of this hot rock collect
in the base of the mantle. When a
reservoir is sufficiently large, a sphere
(35) of this hot rock forces its way up
through the upper mantle to Earth’s
surface, creating a broad bulge in the
topography. The “mantle plume” thus
formed, once established, continues to
(40) channel hot material from the mantle
base until the reservoir is emptied.
The surface mark of an established
plume is a hot spot—an isolated
region of volcanoes and uplifted terrain
(45) located far from the edge of a surface
plate. Because the source of a hot
spot remains fixed while a surface
plate moves over it, over a long period
of time an active plume creates a chain
(50) of volcanoes or volcanic islands, a
track marking the position of the plume
relative to the moving plate. The natural
history of the Hawaiian island chain
clearly shows the movement of the
Pacific plate over a fixed plume.
Q23:
It can be inferred from the passage that a chain of volcanoes created by a mantle plume would most likely be characterized by

A. a curved outline
B. constituent volcanoes that differ from each other in age
C. occurrence near a plate boundary where one plate bends under another
D. appearance near many other volcanic chains
E. rocks with a wide range of chemical composition
請問第23題正確選項中的that differ from each other in age這段話我在原文完全對不到
不知道為什麼這是正確選項
謝謝
解析
定位句:
Because the source of a hot spot remains fixed while a surface plate moves over itover a long period of time an active plume creates a chain
of volcanoes or volcanic islands.

從這句得知板塊是會移動的, the source of a hot spot 就是指會一直輸送hot material撞擊地面的mantle plume形成hot pot, 板塊移動時因為plume持續輸送hot material, 所以就會在不同時期形成一連串的hot spot, 所以這裡推論出不同時期形成的hot spot=volcanoes是differ in age, 年齡是不同的

注意推論題是要你"推論", 答案不會在文章中明示