In C₄ Plants, Photosynthesis Operates More Quickly and with Less

In C₄ plants, photosynthesis operates more quickly and with less need for widely open stomata than in C₃ plants. What characteristics of the enzyme PEP carboxylase are responsible for these differences?

A) PEP carboxylase is located in the cytoplasm, so it is in closer contact with its substrate than rubisco, which is located in the chloroplast.
B) PEP carboxylase has a higher catalytic rate than rubisco, which results in an increase in CO₂ concentrations in bundle-sheath cells.
C) PEP carboxylase is a much smaller enzyme than rubisco and, therefore, is present at much higher concentrations in C₄ plant cells.
D) PEP carboxylase is not consumed in its reaction with HCO₃^-.