In human females, an event that reflects the onset of the reproductive phase is

The correct option is D

Menstruation

The correct option is D.

Explanation of the correct option:

1. Menstruation is the periodic reproductive cycle that occurs in females after a period of 28-29 days.
2. It involves 4 phases:
   1. Menstrual phase: When the uterus lining which was prepared for implantation starts to shed. This occurs for 3-5 days.
   2. Follicular phase: A mature egg is released from each of the ovaries per month. This causes the uterus to start preparing for expected implantation.
   3. Ovulatory phase: Ovulation occurs around the 13th day. This period is ideal in the case of conception.
   4. Luteal phase: in this phase, if fertilization occurs, pregnancy begins else the menstrual cycle begins all over again.

Explanation of the ncorrect option:

Option A:

Growth in the body includes an increase in the height & weight of an individual.

Option B:

Changes in hair patterns is a type of secondary growth.

Option C:

During adolescence stage, one can generally notice the prominent changes in body of an individual, which is known as puberty. The changes which are seen during the adolescence period are:

1. Change in voice.
2. Change in the body shape.
3. Change in the hormonal levels.
4. Development of the secondary sexual organs.
5. Increase in secretion from sweat and sebaceous glands.

Final answer: In human females, an event that reflects the onset of the reproductive phase is menstruation.