求助：GWD-TN-18 - ChaseDream - Powered by Discuz!

Manatees, aquatic mammals inhabiting Florida’s rivers and coastal waters, swim close to the surface and are frequently killed in collisions with boats.To address the problem, boat traffic in manatee-populated waters is being required to maintain very low speeds.Unfortunately, manatees are unable to hear low-pitched sounds and a boat’s sound lowers in pitch as the boat slows.Therefore, this approach may in fact make things worse rather than better.

Which of the following, if true, casts most doubt on the conclusion?

A.The areas where boats would have to maintain low speeds were decided partly on the basis of manatee-population estimates and partly from numbers of reported collisions between manatees and boats.

B.Because the water hyacinth that manatees feed on grows best in water that is nearly still, water hyacinth beds can be disturbed or damaged by fast-moving boat traffic.

C.Over the last several decades, boat traffic in Florida’s coastal waters has been increasing almost continuously and now represents the greatest threat to the endangered manatee population.

D.The sound of a boat engine generally travels much further under water than it does through the air.

E.When experimenters exposed manatees to the recorded sounds of boats moving at various speeds, the creatures were unable to discern the sounds over normal background noise.
答案是：E.我没读懂，E怎么削弱了~

22. GWD27-Q22:

Whales originated in the freshwater lakes and rivers of ancient Asia about sixty million years ago.Not until about ten million years later did species of whales develop specialized kidneys enabling them to drink salt water.Although fossil evidence shows that some early whale species that lacked such kidneys sometimes swam in the Earth’s saltwater oceans, these species must have had to return frequently to freshwater rivers to drink.

Which of the following is most strongly supported by the information given?

A.Fossils of whale species dating from between sixty million and fifty million years ago will not be found on continents that were at the time separated from ancient Asia by wide expanses of ocean.

B.Among whale fossils that date from later than about fifty million years ago, none are fossils of whale species that drank only fresh water.

C.Fossils of whale species that drank fresh water will not be found in close proximity to fossils of whale species that drank salt water.

D.The earliest whales that drank salt water differed from fresh-water-drinking whales only in their possession of specialized kidneys.

E.Between sixty million and fifty million years ago, the freshwater lakes and rivers in which whales originated were gradually invaded by salt water.