The answer is; D
A balanced equation is one that observes the law of thermodynamics on the conservation of matter and energy. Matter or energy cannot be created or destroyed but can only be transformed.
In this equation, therefore, the number of elements on the right side of the equation should match those of the left side. Of the choice equations, this is a balanced one; 6CO2 + 6H2O --> C6H12O6 + 6O2 and one that reflects the process of photosynthesis.