The graph below shows the levels of estrogen and progesterone over the course of the menstrual cycle. 
What event is caused by the rapid decrease in hormones in the region indicated by the arrow in the upper right portion of the graph?
Definitions:
Linguistic Ability
The capacity to use language effectively for communication, which includes the abilities to speak, write, listen, and read.
Grooming Customs
Traditional or customary practices related to personal hygiene and appearance maintenance followed by individuals or cultures.
Courtship Customs
Social behaviors and practices observed in the process of seeking a partner for romance or marriage.
Numerical Order
A method or system of arranging or understanding numbers in a sequence based on their value.
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