The correct statement$(s)$ related to oxoacids of phosphorus is(are):
$(A)$ Upon heating,$H_3PO_3$ undergoes disproportionation reaction to produce $H_3PO_4$ and $PH_3$.
$(B)$ While $H_3PO_3$ can act as a reducing agent,$H_3PO_4$ cannot.
$(C)$ $H_3PO_3$ is a monobasic acid.
$(D)$ The $H$ atom of the $P-H$ bond in $H_3PO_3$ is not ionizable in water.

• A
  $A, B, C$
• B
  $A, B, D$
• C
  $A, B$
• D
  $A, C$