Assertion $(A):$ Regulation of $lac$ operon by repressor is referred to as negative regulation.
Reason $(R):$ Repressor protein binds to the operator region and prevents $\text{RNA}$ polymerase from transcribing the operon.

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