$P_4O_{10}$ is not used to dry $NH_3$ gas because

• A
  $P_4O_{10}$ is neutral
• B
  $P_4O_{10}$ is not a drying agent
• C
  $P_4O_{10}$ is acidic and $NH_3$ is basic
• D
  $P_4O_{10}$ is basic and $NH_3$ is acidic