Amount of oxalic acid present in a solution can be determined by its titration with $KMnO_4$ solution in the presence of $H_2SO_4$. The titration gives unsatisfactory result when carried out in the presence of HCl, because HCl

Question

( A ) reduces permanganate to $Mn^{2+}$
( B ) oxidises oxalic acid to carbon dioxide and water
( C ) furnishes $H^+$ ions in addition to those from oxalic acid
( D ) gets oxidised by oxalic acid to chlorine