This question is best answered by comparing the older law with the reform brought in by the new code, since that comparison is exactly what makes one option correct and the rest incorrect.
Since the BNS carried forward the old punishment scheme and simply added Community Service to it, the range of punishment is simple imprisonment, or fine, or both, or Community Service, which is why that is the correct answer.
Another way to reach the answer is to think about why the legislature would touch a settled offence like defamation at all when drafting a new code, and what that motive tells us about each option.
Judged against the reformative purpose the new code was designed to serve, the option that fits is the one that both retains the older penalties and adds Community Service: simple imprisonment, or fine, or both, or Community Service.