单项选择题

Direction:
Read the following text. Choose the best word or phrase for each numbered blank.
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Earthquake 1 can be triggered by many factors, says Tom Hocking, an expert 2 earthquake 3 the California Institute of Technology. The actual 4 of quake itself is the breaking 5 of rocks at or below the earth’s surface. It is believed by scientists that two of the many reasons are the expansion and contraction of the earth’s 6 and continental drift, which are both 7 processes. So, finding one all-purpose warning 8 is impossible. One reason: quakes start deep in the earth, so scientists can not study them 9 . If an early sign of quake is found, it 10 still be impossible to warn humans 11 of all dangerous quakes. Places like Japan and California are 12 with hundreds, if not thousands, of minor faults.
Prediction would be less important if scientists could easily build structures to 13 shakes. While engineering on earthquakes has improved 14 in the past 10 to 15 years, every new quake reveals new weaknesses 15 "quake-resistant" structures, says an expert at Brown University. In Kobe, for example, a highway that opened only last year was 16 . In the Northridge earthquake, on the other hand, well- 17 structures generally did not collapse.
A recent report in Science adds yet more anxiety 18 life on the faulty lines. Researchers ran computer simulations to see how quake-resistant buildings would fare in a moderate-size earthquake, taking into 19 that much of a quake’s energy travels in a large "pulse" of focused shaking. The results: both steel- 20 buildings and buildings that sit on insulating rubber pads suffered severe damage.