A.  Leaves respire and utilize O2 and release CO2.
B.  Photosynthesis and respiration occur at same rate. So there is not net exchange of gases between atmosphere and plants.
C.  Rate of photosynthesis increases, so do the O2 production, with a net release of oxygen coupled with the uptake of CO2.
D.  Rate of respiration becomes more than rate of photosynthesis.