What day is considered to be the first day of a female's reproductive cycle?
When hormone levels are low and the uterus lining is shed.
When hormone levels are high and the uterus lining is shed.
When hormone levels are low and the ovary releases an egg.
When hormone levels are high and the ovary releases an egg.

When hormone levels are low and the uterus lining is shed.

Explanation:

The first day of menstruation - the day whenthe uterus lining starts to be shed. This is induced by a low level or hormones (this is also why some women feel down during this time)

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