Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.

Assertion $A$: Endometrium is necessary for implantation of blastocyst.

Reason $R$: In the absence of fertilization, the corpus luteum degenerates that causes disintegration of endometrium.

In the light of the above statements, choose the correct answer from the options given below:

• A

  $A$ is false but $R$ is true.

• B

  Both $A$ and $R$ are true and $R$ is the correct explanation of $A$.

• C

  Both $A$ and $R$ are true but $R$ is NOT the correct explanation of $A$.

• D

  $A$ is true but $R$ is false.