Considered as a continuous body of fluid, the atmosphere is another kind of ocean. Yet, in 11 of the total amount of rain and snow on land areas in the course of a year, one of the most 12 facts is the very small amount of water in the atmosphere at any given 13 . The volume of the lower seven miles of the atmosphere—the realm of weather events—is 14 four times the volume of the world's oceans. But the atmosphere 15 very little water. It is chiefly in the form of 16 vapor, some of which is carried over land by air currents. If all vapor 17 fell, it would form a layer only about one inch thick. A heavy rainstorm on a given area may use up only a small percentage of the water from the air mass that passes over.
　　How, then, can some land areas receive more than 400 inches of rain per year? How can several inches of rain fall during a single storm in a few minutes or hours? The answer is that rain-yielding air masses are in 18 , and as the driving air mass moves on, new mist air takes its place.
　　The basic source of most water vapor is the ocean. Evaporation, vapor transport, and rainfall make up the 19 movement of water from ocean to atmosphere to land and back to the sea. Rivers return water to the sea. In an underground area of the cycle,   flowing bodies of water 20 some water directly into rivers and some directly to the sea.

　　A. contains     B.    view       C.    discard    D.    movement
　　E. time    F.    amazing  G.    continuous      H.    roughly
　　I.  amusing    J.     motion    K.    rudely     L.    vision
　　M.  invisible  N.    suddenly  O.    discharge
　　
　　答案：11.   B    12. F    13. E    14. H   15. A   16. M   17.  N   18. J     19. G   20. O