【分析解答题】

WATERThe 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 ofthe 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 toout 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 theoceans. 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 undergroundwater as is actually on the surface. There is also a minor,but extremely important, fraction of the water supplywhich is present as water vapor in the atmosphere.