The correct option is A C4 plants will have a lower CO2 compensation point
CO2 compensation point is the concentration of CO2 at which the amount of CO2 consumed during photosynthesis is equal to the concentration of CO2 released during the various processes of respiration.
In case of C3 plants, CO2 is produced by photorespiration and cellular respiration.
Whereas in case of a C4 plant, photorespiration doesn't occur due to CO2 concentrating mechanisms and CO2 is produced only by cellular respiration.
Hence, in C3 plants, higher CO2 concentration is needed for carboxylase activity of RuBisCO and to prevent photorespiration.
Whereas C4 plants can carry out photosynthesis at even low CO2: O2 concentration ratios.
Hence, C4 plants will require a lower CO2 concentration for photosynthesis and, in turn, will have a lower compensation point.