The overall process of photosynthesis
a. results in the reduction of $\mathrm{CO}_{2}$ and the oxidation of $\mathrm{H}_{2} \mathrm{O}$.
b. results in the reduction of $\mathrm{H}_{2} \mathrm{O}$ and the oxidation of $\mathrm{CO}_{2}$.
c. consumes $\mathrm{O}_{2}$ and produces $\mathrm{CO}_{2}$.
d. produces $\mathrm{O}_{2}$ from $\mathrm{CO}_{2}$.