$P -$ Assertion: Blue-green algae are prokaryotic algae.
$Q -$ Reason: Ribosomes in blue-green algae are of the $70S$ type.

• A
  $P$ (Assertion) and $Q$ (Reason) are both true,and $P$ is the correct explanation of $Q$.
• B
  $P$ (Assertion) and $Q$ (Reason) are both true,but $P$ is not the correct explanation of $Q$.
• C
  $P$ (Assertion) is true,but $Q$ (Reason) is false.
• D
  $P$ (Assertion) is false,but $Q$ (Reason) is true.