The correct option is A Lower rate of photorespiration.
In C3 plants, CO2 is pumped directly into the Calvin cycle, leaving rubisco exposed to O2. Rubisco in a C3 will take up O2 rather than CO2 to undergo photorespiration. Photorespiration occurs under low concentrations of CO2 and high concentrations of O2. This process reduces efficiency of photosynthesis, potentially reducing photosynthetic output by 25% in C3 plants. C4 plants capture carbon dioxide in their mesophyll cells forming oxaloacetate. This oxaloacetate is then converted to malate and is transported into the bundle sheath cells, where oxygen concentration is low to avoid photorespiration. So, C4 plants are more efficient in photosynthesis than C3 plants. Thus, option A is correct.