There is a little difference in acid strength in the series `H_3 PO_4, H_3 PO_3` and `H_3 PO_2` because
A. Phosphorus in theses acids exists in defferent oxidation states
B. Number of unprotonated oxygen atoms responsible for increase of acidity due to inductive effect remains the same
C. Phosphorus is not a highly electronegative element
D. Phosphorus oxides are less basic
