What causes an earthquake?
     An earthquake is caused by rocks moving underground. The surface of the earth is made up of about 20
huge plates. The plates are thousands of miles wide and many miles thick. Like turtles with their shells, they
carry oceans and continents right on their backs.
     All the earth's plates are constantly in motion, although they move very slowly, maybe an inch a year. They
push each other, trying to slip under or over each other, or to slide past one another. Earthquakes often happen
when two plates come together. Along the plates where the plates meet, there is a kind of crack in the earth's
surface called a fault. The most famous fault in the United States is the San Andreas Fault, which runs 600 miles
through California and is more than 30 million years old.
     An earthquake happens along a fault where two plates rub together while moving in different directions. The
earth shakes and shivers and vibrates like a rubber band that's been snapped. Those vibrations are picked up by
an instrument which enables experts to figure out where the earthquake occurs and how strong it is. Scientists
measure an earthquake's strength by what they have named the Richter Scale. The Scale runs from zero to nine,
with nine being the most powerful. Sometimes an earthquake occurs so far below the surface, we can hardly
feel it on top. Sometimes an earthquake is so strong that it has more power than a nuclear explosion. An
earthquake can last five seconds or up to ten minutes and create enough heat to melt any rock.
(Help: 1. plate n.板块 2. turtle n.海龟 3. shell n.壳 4. constantly adv.不断地 5. occur v.发生
         6. rub v. 摩擦 7. vibrate v. 振动 8. figure out计算出 9. measure v. 测量 10. melt v. 熔化)

根据文章内容判断下列句子的对(T)与错(F)。
(     )1. An earthquake is caused by rocks moving underground.
(     )2. All the earth's plates are constantly in motion, and they move very fast.
(     )3. The most famous fault in the United States is the San Andreas Fault, which runs 600 miles through
           California.
(     )4. The Scale runs from zero to nine, with zero being the most powerful.
根据文章内容，回答下列问题。
5. When can an earthquake occur according to the passage?
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6. How strong can an earthquake sometimes be? 
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7. What is your feeling if an earthquake occurs far below the surface of the earth? 
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