四级练习2012.09.25
[audio]http://sound.yywz123.com/tingbbs/cet4/cet420120925.mp3[/audio]Scientists have discovered a lake in southwest Florida that is thousands of years old. Discovers made there have led scientists to believe this is one of the most important (1)_______________. At the bottom of the lake,they have found bones of now extinct animals that were killed and cooked for food by humans over 12,000 years ago. A hunting device was discovered one of the oldest ever found. This great quantity of human remains and plant and animal fossils gives the scientists a rare chance to study combinations of climate, and (2)________________. The lake is at least 240 feet deep at one point.(3)__________________.This has helped to preserve specimens in the lake that would usually have been destroyed. Because several types of animals were found that are now extinct,it raises several questions among scientists.Did these animals die of natural causes,or were they hunted into extinction by human beings?
**** Hidden Message ***** 1. diaries with studies of ancient man, animals and climate in North America
2. ecology that prepare the way for huamn survival in America
3. it is reaching middle root and contains very little oxygen
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