Final Answer:
The term that best describes the probability level when something happens sporadically but is not uncommon is a) "Occasionally."
Step-by-step explanation:
A) Occasionally - This term suggests that the event happens from time to time but without regular frequency. It aligns with the description of an event that is sporadic yet not uncommon.
B) Frequently - This term implies that the event occurs often, which is more than what "sporadically" suggests.
C) Rarely - This term would indicate that the event does not happen often, which contrasts the idea that it is not uncommon.
D) Always - This term would suggest that the event happens constantly, without fail, which does not fit the description of happening sporadically.
Therefore, the correct answer is A) Occasionally, as it most accurately reflects an event that happens now and then without being rare or frequent.