Identify the principal role of photosynthesis. to convert kinetic energy into the chemical energy of sugars to convert solar energy into the chemical energy of sugars to convert the chemical energy of sugars into the chemical energy that fuels life's processes to convert the chemical energy of sugars into heat to maintain an elevated body temperature

Answer is: to convert solar energy into the chemical energy of sugars.
Solar energy is stored in chemical bonds of sugars (glucose for example). 
In carbon dioxide, carbon has oxidation number +4 and in photosynthesis carbon gain electrons (solar energy), so his oxidation number is lowered (reduced). Light energy is transformed into chemical energy, that is stored in carbohydrate molecules (glucose), which are synthesized from carbon dioxide and water.