Considered as a continuous body of fluid, the atmosphere is another kind of ocean. Yet, in
The basic source of most water vapor is the ocean, evaporation, vapor transport, and precipitation (陈雨) make up the continuous movement of water from ocean to atmosphere to land and back to the sea. Rivers return water the sea. In an underground arc (弧) of the cycle, flowing bodies of water discharge some water directly into rivers and some directly to the sea.
What might have been discussed before this passage?
A.The ocean.
B.The earth.
C.The rainfall.
D.The atmosphere.