I can assure you that cheating is not a regular occurrence at this school.我可以向你保证，考试作弊在本校不常发生。The occurrence of the disease is low. 这种疾病不常发生。Disturbances are relatively infrequent in our prisons.相对来说，我们这里的监狱不常发生骚乱。Earthquakes are not common in this part of the world.地震在这一带不常发生。