2023年12月4日发(作者：)
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大学英语六级听力讲座专项强化真题试卷2
(题后含答案及解析)
题型有：1.
听力原文：Governments, private groups and individuals spend billions of dollars
a year trying to root out non-native organisms that are considered dangerous to
ecosystems and to prevent the introduction of new intruders. ［16］ But a number of
scientists question the assumption that the presence of alien species can never be
acceptable in the natural ecosystem. They say that portraying introduced species as
inherently bad is an unscientific approach. ［17］ “Distinctions between exotic and
native species are artificial,” said l Rosensberg, a professor of evolutionary
biology at the University of Arizona. Because they depend on picking a date and
calling the plants and animals that show up after that date exotic. “Ecosystem’s free
of species to find as exotic are by default considered the most natural. You can’t roll
back the clock and remove all exotics or fix habitats,” berg said. Both
native and exotic species can become invasive and so they all have to be monitored
and controlled when they begin to get out of hand. At its core, the debate is about how
to manage the world’s remaining natural ecosystems and about how and how much to
restore other habitats. Species that invade a territory can harm ecosystems, agriculture
and human health. They can threaten some native species or even destroy and replace
others. “Next to habitat loss, these invasive species represent the greatest threat to
biodiversity worldwide,” many ecologists say. Ecologists generally define an alien
species as one that people accidentally or deliberately carried to its new location.
Across the American continents, exotic species are those introduced after the first
European contact. That date rounded up to 1500 AD represents what ecologists
consider to have been in major shift in the spread of species including crops and
livestock, as they begin to migrate with humans from continent to continent. ［18］
“Only a small percentage of alien species cause problems in their new habitats,”
said Don Smith, professor of ecology and evolutionary biology at the University of
Tenacy. “Of the 7,000 alien species in the United States, out of a total of 150,000
species, only about 10% are invasive,” he pointed out. The other 90% have fit into
their environment and are considered naturalized. Yet appearances can deceive,
ecologists caution, and many of these exotics may be considered acceptable only
because no one has documented their harmful effects. What is more, non-native
species can appear harmless for decades then turn ons 16 to 18 are
based on the recording you have just assumption about introduced
species is challenged by a number of scientists? does l Rosensberg
think of the exotic and native species? does Professor Don Smith say about
alien species?
1．
A．They will root out native species altogether.
B．They contribute to a region’s biodiversity.
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