题目原文：
The zebra mussel, a freshwater shellfish native to Eastern Europe, has long been spreading out from its original habitats and has now reached parts of North America. There are reasons to believe that this invasion cannot be stopped and that it poses a serious threat to freshwater fish populations in all of North America.
First, the history of the zebra mussel’s spread suggests that the invasion might be unstoppable. It is a prime example of an invasion made possible by human transportation. From the zebra mussel，s original habitats in Eastern Europe, ships helped spread it out along new canals built to connect Europe’s waterways. The mussel can attach itself to a ship’ s bottom or can survive in the water—called “ballast water”—that the ship needs to take on to properly balance its cargo. By the early nineteenth century, the mussel had spread to the whole of Europe. It was later carried to the east coast of North America in the ballast water of ships traveling from Europe. The way ships have spread the zebra mussel inthe past strongly suggests that the species will soon colonize all of North America.
Moreover, once zebra mussels are carried to a new habitat, theycan dominate it. They are a hardy species that does well under a variety of conditions, and they have a high rate of reproduction. Most important, however, zebra mussels often have no predators in their new habitats, and species without natural predators are likely to dominate their habitats.
Finally, zebra mussels are likely to cause a decline in the overall fish population in habitats where they become dominant. The mussels are plankton eaters, which means that they compete for food with manyfreshwater fish species.
题目音频：
学术写作：
教授：政府是否应该资助太空探索？
Kelly：不应该。太贵，没有直接好处。
Andrew：应该。很多发明来源于太空探索。
Doctor Achebe:
This week, we will be discussing space exploration. Some people think that it is a waste of money for governments to fund space exploration. Others disagree with this view arguing that space exploration is a valuable and necessary investment for our future. They think that it is worthy for governments to fund space exploration. I want to know what you think about this topic. Do you think that governments should fund space exploration? Why or why not?
Kelly:
I don’t think that governments should fund space exploration because it will be too costly to build spaceships and develop related technologies. Though space exploration tech costs billions, it doesn’t offer direct benefits to most people, which makes its funding a controversial issue.
Andrew:
Personally, I do think that all the costs will be worth it. The potential scientific discoveries and technological advancements could have far-reaching impacts that justify the initial investment. Imagine the new inventions that might come from this exploration. Such technology could greatly improve our everyday lives.
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