Under the world's oceans and seas lies an attracting world of lands that stretches hundreds of kilometres in every direction. In this world，without the sun，there are deep canyons(峡谷)，great plains，and towering ranges of mountains. And this underwater world covers 70 percent of the earth's surface.

　　The world's longest mountain range extends 16,000 kilometres under the Atlantic Ocean from Iceland to the Antarctic. Called the Mid­Atlantic Ridge(山脊)，this range of mountains contains a number of high peaks，among them are the Ascension Island，the Azores，and Iceland.

　　The world's highest mountain is found in the mid­Pacific area. It is the Hawaiian volcano Mauna Kea，which is 9,450 metres from base to peak. This is nearly 610 metres taller than Mount Everest. Only 4,221 metres of Mauna Kea rises above the surface of the sea. In 1873 the British survey ship Challenger discovered the deepest trench(海沟) in all the seas. Named the Challenger Deep，it is near the island of Guam and is 11 kilometres deep.

　　Since sunlight only reaches to a depth of about 244 metres，many of the creatures of the deep sea live in a world of darkness. However，to get help in their survival，many have their own bright lighting system. Food comes to them from the upper levels of the ocean and they can get a constant supply from the waste matter that gradually moves downward toward the ocean floor. These undersea creatures must remain at the various places for which they are fit. To wander to other levels could result in death from improper water pressure.

14．The best title for this text should be .

A．The Sunless World B．The Longest Mountain

C．The Highest Mountain D．The Deepest Trench

15．The world's longest mountain range under the ocean .

A．extends 1,600 kilometres under the Atlantic Ocean

B．is called the Mid­Atlantic Ridge

C．contains few high peaks

D．extends from Iceland to the Azores

16．From this passage we know that .

A．the longest and the highest mountains lie in the sea

B．the highest mountain lies on land

C．the longest mountain lies on land

D．Mauna Kea is 4,221 metres high