WATER The second most important constituent of the biosphere is liquid water. This can only exist in a very narrow range of temperatures, since water freezes at 0℃ and boils at 100℃. This is only a tiny range compared with the low temperatures of some other planets and the hot interior of the earth, let the temperature of the sun. 　　　　　　　　　　 (1)__________ As we know, life would only be possible on the face　　　　　　(2)__________ of a planet had temperatures somewhere within this range.　　　 (3)__________ The earth’’s supply of water probably remains quite fairly　　　 (4)__________ constant in quantity. A certain number of hydrogen atoms, which are one of the main constituents of water, are lost by escaping from the atmosphere to out space, but they are probably just about replaced by 　 　　 (5)__________ new water rising away from the depths of the earth during 　 　 (6)__________ volcanic action. The total quantity of water is not known, and it is about enough to cover the surface of the globe 　　　 (7)_________ to a depth of about two and three-quarter kms. Most of itD97%Dis in the form of the salt waters of the oceans. The rest is fresh, but three quarter of this is 　 　　 (8)_________ in the form of ice at the Poles and on mountains, and cannot be used by living systems when melteD．Of the 　　 (9)_________ remaining fraction, which is somewhat fewer than 1% of the　 　 (10)__________ whole, there is 10D20 times as much stored as underground water as is actually on the surface. There is also a minor, but extremely important, fraction of the water supply which is present as water vapor in the atmosphere.