题目内容
根据霍夫曼定理，当霍夫曼比例小于1时，意味着（）。
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The passage suggests that the fact that "only one community cancer cluster bas ever been traced to all environmental cause" (in the third paragraph) is most likely due to the______.
By using the phrase "the human quality of technology"(Line 5, Para. 2), the author refers to the fact that technology______.
There are two great mysteries about the beach. One is why human beings flock there by thousands, only to prostrate(俯卧) themselves in dense packs of glistening flesh. The other is why the sand goes there. Strange as it seems, oceanographers have never really understood why sand piles up on the shore. Now Douglas Inman and Daniel Conley think they have solved the puzzle.
The puzzle had to do with waves. Though it might seem intuitive that waves carry water to shore, and sand along with it, it's not that simple. The crest(浪尖)of a passing wave lifts a given hit of water upward and landward, but the ensuing trough(波谷) pushes the water back down and Out to sea. Near the bottom, there the sand is, the water was always assumed to just slide back and forth—and the sand with it. "If you take a very aloof look at a beach," says Inman, "you'll realize that if the two motions move sand back and forth the same amount, then all the sand should end up in deep water.'
So for beaches to exist, the crest's onshore flow must somehow move enough sand up the beach to counter the seaward tug of both the trough and gravity . The pressure changes in the sand bed, Inman and Conley think, are the key to beach creation. They found that sand doesn't just slide back and forth with each passing wave. Under a trough, it does slide seaward, in a thin layer just above the bottom. But under a crest its movement is often more elaborate. The higher pressure under a crest—higher because the water is piled higher—forces water into the porous(多孔的) sand. This creates strong whirlpools just above the sand, which help loosen it. As the crest passes overhead, the sand first rushes across the bottom; then it abruptly turns violent lifting off the bottom in large, boiling bunches. Finally, just after the crest passes, the sand explodes up into the great water column. The boiling and rushing move more sand than the backsliding under a trough, so there's a net movement of sand toward the shore.
What is the primary purpose of this passage？
张先生于生日当晚约了好友到某家知名酒楼庆贺。饭局过半，张先生上了趟洗手间，不料洗手间周围地面湿滑，加之灯光昏暗，故不慎踩滑摔伤。经查，地面湿滑系水管老化破裂所致，该酒楼几日前发现该问题但未及时修理。张先生要求该酒楼支付其医疗费未果，遂诉至法院，法官根据《最高人民法院关于审理人身损害赔偿案件适用法律若干问题的解释》第6条第1款的规定：“从事住宿、餐饮、娱乐等经营活动或者其他社会活动的自然人、法人、其他组织，未尽合理限度范围内的安全保障义务致使他人遭受人身损害，赔偿权利人请求其承担相应赔偿责任的，人民法院应予
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