$S$ - Statement: Ligases are enzymes that catalyze the linking of two compounds together.
$R$ - Reason: Isomerases are enzymes that catalyze the inter-conversion of optical,geometric,or positional isomers.

• A
  $S$ and $R$ are both true,and $R$ is the correct explanation of $S$.
• B
  $S$ and $R$ are both true,but $R$ is not the correct explanation of $S$.
• C
  $S$ is true and $R$ is false.
• D
  $S$ is false and $R$ is true.