During the water cycle, water from rivers, streams, lakes, and oceans evaporate into water vapor . Then, the water vapor rises into the cool atmosphere and condenses into precipitation . For evaporation to occur, heat and energy must be added to the cycle. Where does this heat and energy come from ? A. Volcanic eruptions
B. The sun
C. The earths core
D. Global warming

the sun

Explanation:

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-