What type of volcanic activity is represented by a volcanic eruption that occurs in a fairly regular interval?

The correct choice is characterized by volcanic eruptions that occur at fairly regular intervals. This means that the volcano is showing a pattern of activity where eruptions happen sporadically but with some consistency over time. This type of activity suggests that the volcano is still alive and has potential for future eruptions.

Active volcanoes continuously erupt or show significant signs of activity. Dormant volcanoes have not erupted for a long time but could potentially erupt again; they lack the regular pattern that intermittent volcanoes exhibit. Extinct volcanoes are those that are not expected to erupt again in the future due to a lack of magma supply. Therefore, the term "intermittent" best describes volcanic eruptions that occur with some regularity but are not constant, distinguishing it from the other types of activity.