Persephone leaves the underworld in Spring and she returns in the beginning of Fall.
Persephone ate of the pomegranate in the Underworld and so had to return to the Underworld every year.
Persephone had ate the pomegranate the food of the Underworld.
Persephone ate of the pomegranate in the Underworld, and thus every year must go to the Underworld - then return to Earth.
In the myth of Persephone, the climax is when Persephone is abducted by Hades and taken to the Underworld against her will. This event triggers the conflict between Demeter and Hades, leading to the negotiation for Persephone's return.
Persephone had ate the pomegranate in the Underworld; so had to return to the Underworld a part of every year.
The pomegranate.
Every year when Persephone returns from the Underworld her mother Demeter allows Spring to return to the earth.
Persephone stays in the Underworld for half of the year (six months) and is allowed to return to Olympus for the other half.
She had eaten a pomegranate from the underworld which forced her to return.
Kidnapping, most assume, Persephone did the eating of the food of the underworld part, which stuck her in the Underworld; guaranteeing she could never fully return to the world above: but she had to return thus becoming the goddess of spring.
In Greek myth, it is because of the abduction of Persephone that the Earth/we know the seasons: for Persephone also ate of the pomegranate in the Underworld and every year must return between Earth/Olympus and Underworld.
Persephone was celebrated by humans as the return of Spring, and hailed as Queen of the Underworld where the dead dwell after the living died.