A、Iron and copper. B、Gold and copper. C、Nickel and bronze. D、Iron and bronze. A短文提到海床上有很多有价值的矿物质，such as后又以铁、铜作为例子，故选A。

Man is a land animal, but he is also closely tied to the sea Throughout history the sea has served the needs of man. The sea has provided man with food and a convenient way to travel to many parts of the world. Toady, experts believe that nearly two-thirds of the world’s population live within eighty kilometers of the seacoast. [23]In the modern technological world, the sea offers many resources to help mankind survive. Resources on land are beginning to grow less. The sea, however, still offers hope to supply many of man’s needs in the future. The riches of the sea yet to be developed by man’s technology are impressive. Oil and gas explorations have existed for nearly thirty years. [24]Valuable amounts of minerals such as iron, copper exist on the ocean floor. Besides oil and gas, the seas may offer new sources of energy. For example, warm temperature of the ocean can be used as the steam in a steamship. Sea may also offer a source of energy as electricity for mankind. Technology is enabling man to explore even deeper under the sea. It is obvious that the technology to harvest the sea continues to improve. [25]By the 2050, experts believe that the problems to explore the food, minerals and energy resources of the sea will have been largely solved.
23. What do we learn about the sea in the modern technological world?
24. What kind of minerals can we find on the ocean floor?
25. What do the experts believe will happen by the year 2050?