cycle

Cycle means a series of actions or events that repeats itself on a regular basis.

Cycle can be used as a noun or a verb. In this exercise, cycle is used as a noun.

For example:

There are four stages in the life cycle of a butterfly.

Spring, summer, autumn and winter make up the cycle of the seasons.

We see the full moon when it is in the middle of its cycle, but we see only a small part of the moon at the beginning or end of its cycle.