In compound sentence, there are two independent clauses that are joined using a coordinator. While in complex sentence, there are two or more clauses with one essentially an independent clause while there can be on or more dependent clauses. The difference between compound and complex sentence is that there is no dependent clause in compound sentence and at least there is one dependent clause in complex sentence.
The theme of night calls is a dark theme
The only preposition in the options available to you is of, so the correct answer is C.
A) and B) are conjunctions.
D) is an adverb.
