$P$: Monosaccharides can pass through the cell membrane.
$Q$: Monosaccharides are the simplest carbohydrates.

• A
  Statement $P$ is true but statement $Q$ is false.
• B
  Both statements $P$ and $Q$ are true,but statement $Q$ is not the correct explanation of $P$.
• C
  Both statements $P$ and $Q$ are true,and statement $Q$ is the correct explanation of $P$.
• D
  Both statements $P$ and $Q$ are false.