What is the mean oxidation number of sulfur in each compound?
- ACa(HSO$_3$)$_2$: $4$ and Na$_2$S$_2$O$_3$: $2$
- BCa(HSO$_3$)$_2$: $4$ and Na$_2$S$_2$O$_3$: $4$
- CCa(HSO$_3$)$_2$: $6$ and Na$_2$S$_2$O$_3$: $2$
- DCa(HSO$_3$)$_2$: $6$ and Na$_2$S$_2$O$_3$: $4$