$A$: In metatherians,the scrotum is present in front of the penis.
$R$: In prototherians,the scrotum is present behind the penis.

• A
  Assertion and Reason both are correct and Reason is the correct explanation of Assertion.
• B
  Assertion and Reason both are correct but Reason is not the correct explanation of Assertion.
• C
  Assertion is correct,but Reason is incorrect.
• D
  Both Assertion and Reason are incorrect.