cycle

1 - Adolescence is an important phase in the life cycle.

2 - Paper is made from a natural renewable resource, wood, which has the capacity to be produced in an endless cycle.

3 - Poets and authors have frequently written about sunset, a magical time in the daily cycle.

4 - Over timescales of thousands of year, the Earth goes through a natural cycle of warmer and colder periods, driven by changes in heat coming from the Sun.

5 - People will not have conquered the space environment until they can safely complete a life cycle in that setting.