1.) Why does menstruation begin?
2.) How long does the menstrual cycle usually last?
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1.) Why does menstruation begin?

A.) Period happens because of changes in hormones in the body. 

2.) How long does the menstrual cycle usually last?

A.) the menstrual cycle lasts 21 to 35 days while bleeding between 2 to 7 days

-TheUnknownScientist

and after water is usually warmed by the sun the water temperature raises and then evaporates .

carbon atoms, hydrogen, oxygen, and nitrogen.