The correct option is A Bundle sheath
In C4 plants, the Calvin cycle takes place in the bundle sheath, whereas in C3 plants it takes place in mesophyll cells.
In C4 plants, phosphoenolpyruvate (PEP) accepts CO2 in the mesophyll cells. The mesophyll cells lack the RuBisCO enzyme. On accepting CO2, PEP gets converted to oxaloacetic acid in the presence of the enzyme phosphoenolpyruvate carboxylase (PEPcase). Oxaloacetic acid is then converted to malic acid. This malic acid is transported to the bundle sheath. The plasmodesmata between the bundle sheath and the mesophyll cells allows malic acid to pass through. The bundle sheath cells are rich in the RuBisCO enzyme but lack PEPcase. The malic acid undergoes decarboxylation in the bundle sheath and releases CO2. The CO2 that is released then goes into the C3 cycle.