In some plants, the first stable product after the fixation of CO₂ is a 4 carbon dicarboxylic acid called Oxaloacetic acid (OAA). Such plants are called C₄ plants. Examples are sugarcane, maize, some other monocot and dicot plants.

C₄ plants have characteristic leaf anatomy and dimorphic Chloroplasts: 

1. The leaf mesophyll consists of compactly packed cells and is not differentiated into palisade and spongy mesophyll.

2. The vascular bundles in leaves are surrounded by distinct bundle sheath of radially enlarged parenchyma cells.

3. The Chloroplasts in leaves are dimorphic: granal and agranal chloroplasts.

Chloroplasts in the mesophyll cells are smaller and possess grana and chloroplasts in the bundle sheath cells are larger and without grana.

This type of anatomy in C₄ plants is called Kranz anatomy 

Unlike C₃ plants, photosynthesis of C₄ plants is not inhibited by O₂. 

They have a very low CO₂ compensation point which is the ambient CO₂ concentration at which the rate of CO₂ uptake (for photosynthesis) is balanced by the rate of CO₂ evolution. For C₃ plants it's value is 20-100μ l/litre and for C₄ plants it's value is 0-5 μl/litre.

So, bundle sheath cells have the CO₂ concentrating mechanism and there is suppression of photorespiratory loss of CO₂. Therefore C₄ plants have better photosynthesizing power than  C₃ plants.

So, the correct answer is B.