練習(xí)題-2

Part Ⅲ Reading Tasks

True／False／Not Given Exercises

Unit2

　　When was the last time you saw a frog? Chances are, if you live in a city, you have

not seen one for some time. Even in wet areas once teeming with frogs and toads, it is

becoming less and less easy to find those slimy, hopping and sometimes poisonous

members of the animal kingdom. All over the world, and even in remote parts of Australia,

frogs are losing the ecological battle for survival, and biologists are at a loss to explain

their demise. Are amphibians simply oversensitive to changes in the ecosystem? Could it

be that their rapid decline in numbers is signaling some coming environmental disaster for us all?

　　This frightening scenario is in part the consequence of a dramatic increase over the

last quarter century in the development of once natural areas of wet marshland; home not

only to frogs but to all manner of wildlife. However, as yet, there are no obvious reasons

why certain frog species are disappearing from rainforests in Australia that have barely

been touched by human hand. The mystery is unsettling to say the least, for it is known that

amphibian species are extremely sensitive to environmental variations in temperature and

moisture levels. The danger is that planet Earth might not only lose a vital link in the

ecological food chain (frogs keep populations of otherwise pestilent insects at manageable

levels), but we might be increasing our output of air pollutants to levels that may have

already become irreversible. Frogs could be inadvertently warning us of a catastrophe.??

　　An example of a species of frog that, at far as is known, has become extinct, is the

platypus frog. Like the well-known Australian mammal it was named after, it exhibited

some very strange behaviour; instead of giving birth to tadpoles in the water, it raised its

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