$A$: Corticotrophin-releasing hormone is a part of the clock that establishes the timing of birth.
$R$: The signals for parturition originate from the fully developed foetus and placenta,which induce mild uterine contractions called the foetal ejection reflex.

• 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.