Cyclic changes in hormones. Signs and symptoms of premenstrual syndrome change with hormonal fluctuations and disappear with pregnancy and menopause.
激素周期变化。经前综合症的体征和症状随着激素的变化而发生变化，而在妊娠期和更年期的时候会消失。
2
And it's an extremely short segment within an eternally long natural cyclic pattern of change that continues to occur independent of our presence or approval.
Other environmental pressures to the reef and its ecosystem include water quality from runoff, climate change accompanied by mass coral bleaching, and cyclic outbreaks of the crown-of-thorns starfish.