A、They were mostly endangered. B、They were limited. C、They would never be exhausted. D、They were difficult to recover. C选项中的they

During the nineteenth century, when little was known about environmentalism and conservation, it was common to hear people say that the resources of the sea were unlimited. They believed the world and nature would continuously reproduce all the resources they would need. For example, a noted biologist writing in the mid-nineteenth century commented that none of the great sea fisheries were to be exhausted. Today, though, there is evidence that the resources of the sea are seriously endangered.
    Previously, environmentalists have focused their attention on the land and air. The list of endangered species now includes the African elephant, the Indian tiger and the American eagle. Recently, however, they are beginning to discover that the resources of the sea are in as much danger.
    Furthermore, the threats to fish are more alarming in some ways than the threats to animals and birds. This is because fish are a much more needed food source, and people throughout the world depend on fish as an important part of their diet. Hence, a decline in the fish supply could have extensive effects on hunger and population. Fishermen in the North Atlantic alone annually harvest 20 billion pounds of fish to satisfy food demand, but the world needs to recognise that these practises cannot continue without exhausting fish reserves within the next few years. Rapidly declining sea resources in many parts of the world are problems that cannot be ignored any longer. Unlike the scholars in the nineteenth century, we now know that food supplies in the sea cannot last forever.
Questions 22 to 25 are based on the passage you have just heard.
22. What did many people in the nineteenth century think about sea resources, according to the passage?
23. What can we learn about the African elephant, Indian tiger, and American eagle from the passage?
24. Why are the threats to fish more alarming than other animals?
25. What’s the purpose of the passage?