EXPLAIN THE PERIODS CIRCLE .THANKS I DONT UNDERSTAND IT

A menstrual cycle begins with the first day of your period, or menstruation and starts over again when the next period begins. Throughout a monthly menstrual cycle, your body makes different amounts of chemicals called hormones to prepare for pregnancy.

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.