What are $X$ and $Y$ in the following reactions?

• A

  $X$	$Y$
  Conc. $HNO_3$	$H_2SO_4(SO_3)$

• B

  $X$	$Y$
  Conc. $HNO_3$ + Conc. $H_2SO_4$ / $333 \ K$	$H_2SO_4(SO_3)$

• C

  $X$	$Y$
  $NaNO_2$ / $HCl$	$H_2SO_4$

• D

  $X$	$Y$
  Dil. $HNO_3$	$SO_3$