GWD又一个/GWD-11-27

Mayor:  Migrating shorebirds stop at our beach just to feed on horseshoe-crab eggs, a phenomenon that attracts tourists.  To bring more tourists, the town council plans to undertake a beach reclamation project to double the area available to crabs for nesting.

Birdwatcher:  Without a high density of crabs on a beach, migrating shorebirds will go hungry because shorebirds only eat eggs that a crab happens to uncover when it is digging its own nest.

Which of the following, if true, would provide the mayor with the strongest counter to the birdwatcher’s objection?

1. Every year a certain percentage of crabs are caught by fishermen as bait for eel traps.


2. Horseshoe crabs are so prolific that given favorable circumstances their numbers increase rapidly.


3. On average, tourists who come to the town in order to watch birds spend more money there than tourists who come for other purposes.


4. The additional land made available by the reclamation project will give migrating shorebirds more space.


5. Some of the migrating shorebirds make only one stop during their migration form South America to Canada

Charcoal from a hearth site in Colorado, 2,000 miles south of Alaska, is known to be 11,200 years old.  Researchers reasoned that, since glaciers prevented human migration south from the Alaska-Siberia land bridge between 18,000 and 11,000 years ago, humans must have come to the Americas more than 18,000 years ago.

Which of the following pieces of new evidence would cast doubt on the conclusion drawn above?

1. Using new radiocarbon dating techniques, it was determined that the charcoal from the Colorado site was at least 11,400 years old.


2. Another campsite was found in New Mexico with remains dated at 16,000 years old.


3. A computer simulation of glacial activity showed that it would already have been impossible for humans to travel south overland from Alaska 18,500 years ago.


4. Using new radiocarbon dating techniques, it was proved that an ice-free corridor allowed passage south from the Alaska-Siberia land bridge at least 11,400 years ago.


5. Studies of various other hunting-gathering populations showed convincingly that, once the glaciers allowed passage, humans could have migrated from Alaska to Colorado in about 20 years.

B,D

The answer is B,D.

1.      For the first question, if the crab can produce many offspring,  the density of the crab won’t decline and the reason hold by the birdwatcher won’t sustain.

2. If there do exist a corridor in the glacier period to let the human walk through, then   human did not have to be there 18000 years ago

   第2题原文推理：（1）11000—18000年人无法到那个地点；（2）那个地点有Charcoal ——》人在18000年前就去了那个地点

   D说：11400年前，人可以去那个地点，因此削弱了原文结论