单项选择题

The Pacific Ocean covers more than 166 million square kilometers (more than 64 million square miles) --about one-third of the earth’s surface. The area of the Pacific is greater than that of all of the continents combined, and it makes up nearly half of the area covered by the earth’s oceans.
The Pacific is not only the largest ocean but also the world’s oldest and deepest, with an average depth of 4,280 meters (14,040 feet). Most of the geologic activity of the Pacific occurs around its edges. In fact, the so-called Pacific Ring of Fire contains more than 80 percent of the earth’s active volcanoes and most of its earthquake activity.
The Pacific was given its name because of the tranquillity(安静) of its waters, although it is occasionally swept by typhoons, and a number of strong currents circulate beneath the surface. The influence of the icy Antarctic continent and the smaller ratio of land to sea lowers water temperatures in the southern Pacific slightly in comparison with the northern Pacific.
The commercial importance of the Pacific Ocean has increased significantly since the opening of the Panama Canal, which links the Pacific to the Atlantic Ocean. in 1920. Fishing along the east coasts and near the Equator is a significant industry. The Pacific has also begun to be exploited for its vast mineral resources. The continental shelves off the coasts of California, Alaska, China, and Indonesia are known to contain large reserves of petroleum. Programs are under way to examine the feasibility of mining these deposits.

Programs are under way to examine the（）of mining these deposits.

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