Câu 70. A.as B.whose C.that D.with
VII.Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the best
answer to each of the following questions.
The hard, rigid plates that form the outermost portion of the Earth are about 100 kilometers thick. These plates
include both the Earth's crust and the upper mantle. The rocks of the crust are composed mostly of minerals with light
elements, like aluminum and sodium, while the mantle contains some heavier elements, like iron and magnesium.
Together, the crust and upper mantle that form the surface plates are called the lithosphere. This rigid layer floats on
the denser material of the lower mantle the way a wooden raft floats on a pond. The plates are supported by a weak,
plastic layer of the lower mantle called the asthenosphere. Also like a raft on a pond, the lithospheric plates are carried
along by slow currents in this more fluid layer beneath them.
With an understating of plate tectonics, geologists have put together a new history for the Earth's surface.
About 200 million years ago, the plates at the Earth's surface formed a "suppercontinent" called Pangaea. When this
supercontinent started to tear apart because of plate movement, Pangaea first broke into two large continental masses
with a newly formed sea that grew between the land areas and the depression was filled with water. The southern
one, which included the modern continents of South America, Africa, Australia, and Antarctic, is called Gondwanaland.
The northern one, with North America, Europe, and Asia, is called Laurasi. North America tore away from Europe
about 180 million years ago, forming the northern Atlantic Ocean.
Some of the lithospheric plates carry ocean floor and others carry land masses or a combination of the two types. The
movement of the lithospheric plates is responsible for earthquakes, volcanoes, and the Earth's largest mountain
ranges. Current understating of the interaction between different plates explains why these occur where they do. For
example, the edge of the Pacific Ocean has been called the "Ring of Fire" because so many volcanic eruptions and
earthquakes happen there. Before the 1960's, geologists could not explain why active volcanoes and strong
earthquakes were concentrated in that region. The theory of plate tectonics gave them an answer.
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