In the manufacture of ortho$-$phosphoric acid by strong H$2$SO$4$ leaching wet process, keeping the reactor temperature above $100$C$,$ results in the formation of undesirable

CaSO$4.$ H$2$O and CaSO$4$ crystals

Pyrophosphoric acid

Meta$-$phosphoric acid

All $($A$),($B$)$ and $($C$)$