题目内容：
根据以下材料，回答题"Liquefaction" Key to Much of Japanese Earthquake Damage
The massive subduction zone (俯冲带) earthquake in Japan caused a significant level of soil"liquefaction" (液化设施) that has surprised researchers with its __________ (51) severity, a new analysis shows.
"We've seen localized examples of soil liquefaction as extreme as this before, but the distance and __________ (52) of damage in Japan were unusually severe," said Scott Ashford, a professor of geotechnical engineering at Oregon State University. "Entire structures were tilted and sinking into the sediments (沉淀物) ," Ashford said. "The shifts in soil destroyed water, drain and gas pipelines, crippling the utilities and infrastructure these communities need to __________ (53). We saw some places that sank as much as four feet."
Some degree of soil liquefaction is common in almost any major earthquake. It's a phenomenon in which soils soaked with water, particularly recent sediments or sand, can lose much of their __________ (54) and flow during an earthquake. This can allow structures to shift or sink or __________ (55).
But most earthquakes are much __________ (56) than the recent event in Japan, Ashford said. The length of the Japanese earthquake, as much as five minutes, may force researchers to reconsider the extent of liquefaction damage possibly occurring in situations such as this.
"With such a long-lasting earthquake, we saw __________ (57) structures that might have been okay after 30 seconds just continued to sink and tilt as the shaking continued for several more minutes," he said. "And it was clear that younger sediments, and especially areas built on __________ (58) filled ground, are much more vulnerable."
The data provided by analyzing the Japanese earthquake, researchers said, should make it possible to improve the understanding of this soil __________ (59) and better prepare for it in the future. Ashford said it was critical for the team to collect the information quickly, __________ (60) damage was removed in the recovery efforts.
"There's no doubt that we'll learn things from what happened in Japanl0 thatl 1 will help us to reduce risks in other similar __________ (61)," Ashford said. "Future construction in some places may make more use of techniques known to reduce liquefaction, such as better compaction to make soils dense, or use of reinforcing stone columns."
Ashford pointed out that northern California have younger soils vulnerable to liquefaction—on the coast, near river deposits or in areas with filled ground. The "young" sediments, in geologic terms, may be those __________ (62) within the past 10,000 years or more. In Oregon, for instance, that describes much of downtown Portland, the Portland International Airport and other cities.
Anything __________ (63) a river and old flood plains is a suspect, and the Oregon Department of Transportation has already concluded that 1,100 bridges in the state are at risk from an earthquake. Fewer than 15 percent of them have been reinforced to __________ (64) collapse. Japan has suffered tremendous losses in the March 11 earthquake, but Japanese construction __________ (65) helped prevent many buildings from collapse- even as they tilted and sank into the ground.
回答(51)题 A．internal
B．different
C．difficult
D．widespread
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