Answer : 4. "Occasional"
Explanation :

The most appropriate synonym for "sporadic" in the given sentence is "occasional." "Sporadic" means occurring at irregular intervals or scattered instances, and "occasional" reflects a similar idea of happening from time to time without regularity. The other options, such as "continuous," "indirect," and "repetitive," have different meanings and do not capture the irregular and infrequent nature conveyed by "sporadic."