Sodium carbonate can be manufactured by Solvay's process,but potassium carbonate cannot be prepared by this method because:

• A
  $K_2CO_3$ is more soluble
• B
  $K_2CO_3$ is less soluble
• C
  $KHCO_3$ is more soluble than $NaHCO_3$
• D
  $KHCO_3$ is less soluble than $NaHCO_3$