The correct option is B Presence of large number of chloroplasts in the leaf cells
C4 plants are more efficient in photosynthesis than C3 plants but use more energy. They posses larger number of chloroplasts in the leaf cells.
In the C4 plants, the vascular bundles are surrounded by bundle sheath of larger parenchymatous cells, which in turn are surrounded by mesophyll cells. Chloroplasts in the bundle sheaths are larger and do not contain grana, where as chloroplasts in the mesophyll cells are smaller.