Statement $A$: Large polymeric molecules produced by living organisms have a molecular weight of $10,000 \text{ Daltons}$.
Reason $R$: The valency of carbon is $4$.
Which option is correct for Statement $A$ and Reason $R$?

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