听力原文：In the 19th century it was common to hear people in Europe and America say that t

听力原文： In the 19th century it was common to hear people in Europe and America say that the resources of the sea were unlimited. For example, a noted biologist writing in the mid 1800s commented that all of the great sea-fish industries are inexhaustible. Today there's evidence that the resources of the sea are as seriously threatened as those of the land and the air, and the concern of conservationists now includes sea-fish as well as the African elephant, the Indian tiger and the American eagle. Further, the threat to fish is more alarming in some ways than the threat to birds and land animals because fish are a much needed food resource. Many people throughout the world depend on fish as an important part of their diets, and a decline in the fish supply could have extensive effects on hunger and population.

(23)

A．That they were in infinite.

B．That they should be carefully conserved.

C．That they were declining.

D．That they were limited.