$P$ - Statement: Hemoglobin is a conjugated protein.
$Q$ - Statement: Hemoglobin is an essential protein for the transport of $O_2$.

• A
  Both statements $P$ and $Q$ are false.
• B
  Both statements $P$ and $Q$ are true.
• C
  Both statements $P$ and $Q$ are true. Statement $Q$ is the correct explanation of statement $P$.
• D
  Both statements $P$ and $Q$ are true. Statement $P$ is the correct explanation of statement $Q$.