An egg requires warmth to survive, and first the frog lays the eggs, then the warmth from the sun makes the eggs hatch into baby tadpoles. Given these facts, what heats frog eggs so that they may hatch into tadpoles among the following options:
- sun's heat
 - heat
 - the sun
 - geothermal vents
 - Cooking
 - the mother frog
 - the father frog
 - sunlight


 

   the sun      