$A$ - The salt concentration is less than $5$ (parts per thousand) in inland waters.
$R$ - The salt concentration is $30 - 35$ (parts per thousand) in the sea.

• A
  $A$ and $R$ both are correct.
• B
  $A$ and $R$ both are incorrect.
• C
  $A$ is correct,$R$ is incorrect.
• D
  $A$ is incorrect,$R$ is correct.