The average menstrual cycle is 29 1/2 days, which is exactly the length of the moon's cycle.
(The average menstrual cycle; is; 29 1/2 days, which is exactly the length of the moon's cycle) (29 1/2 days; is; exactly the length of the moon's cycle)
The average menstrual cycle 29 1/2 days
is is
29 1/2 days, which is exactly the length of the moon's cycle
exactly the length of the moon's cycle