填空题

The sea is the largest unknown part of our world. It covers (36) percent of the earth. There is still much to be discovered about this (37) blanket of water.
Some scientists are studying ways of bringing the ocean’s huge (38) of water to the deserts of the world. Others hope to control the weather by learning more about the (39) of heat and moisture between the ocean and the air. Others, are studying the ways in which sound travels and is (40) by water and heat. What happens when seawater touches different elements is another (41) of study.
(42) the ocean floor is an important work among so many interesting studies. (43) , only a very small part of the ocean has been mapped. Now underwater photography is used in mapping parts of the ocean floor. (44) .
If the waters of the ocean could be moved away, the sea floor with its wide valleys, uneven mountains would be an unbelievable sight. Around the edges of the continents the ocean floor is flat and the water is not much deeper than about thirty miles. (45) . But where there are high young mountains along the coast, this flat part may be much less than thirty miles. (46) .