Assertion (A): The zygote formed after fertilisation immediately attaches to the uterus wall.

Reason (R): The uterus wall is always prepared to receive the zygote.

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).

(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).

(c) (A) is true but (R) is false.

(d) (A) is false but (R) is true.

(d) (A) is false but (R) is true.

Explanation: Fertilisation occurs in the fallopian tube, and the resulting single-celled zygote does not immediately attach to the uterus; it must first spend 5 to 7 days undergoing rapid mitotic divisions to transition into a multicellular blastocyst before implantation can occur. The uterine lining (endometrium) dynamically thickens and enriches its blood supply during every menstrual cycle under hormonal control, ensuring the uterus is consistently prepared to receive and nourish a potential embryo.