The answer is D. There was no fog horn to warn away ships from the rocks.
A and B are fragments, not complete sentences. However, if A and B were to be put together, it would be a sentence, but in this case, they are not.
C is a fragment because it doesn't give any information. "A kitchen garden beside the light house", as you can see, it leaves us hanging an also does not have a period.
D is a complete sentence. It has a period, subject, has a main clause, starts with a capital ends with an end mark. There are many other requirements, but those are the main ones for a complete sentence.