Part B Directions: You will hear four dialogues or monologues. Before listening to each one, you will have 5 seconds to read each of the questions which accompany it. While listening, answer each question by choosing A, B, C or D. After listening, you will have 10 seconds to check your answer to each question. You will hear each piece ONLY ONCE. 听力原文： The sea is the largest unknown part of our world. It covers seventy-one percent of the earth. There is still much to be discovered about this vast blanket of water. If the waters of the ocean could be moved away, the sea floor with its wide valleys, irregular fountains and rivers in the sea would be an unbelievable sight. Around the edges of the continents the ocean floor is flat and the water does not become much deeper for about thirty miles. Where there are high young mountains along the coast, this flat part may be much less than thirty miles. But where rivers flow into the sea, the flat area may extend for hundreds of miles. The region near the continents, where the water is not so deep, is the place where you can find a lot of living creatures and plants. Below these living creatures and plants are the largest known quantities of minerals. At the end of the flat part the sea floor suddenly drops down, forming deep hollows that are shaped like bowls. These huge hollows hold most of the world's water. How much percent of the earth does the sea cover?