The correct option is B I love watching horror movies, whereas my friends love watching romantic comedies.
A compound sentence is made up of two independent clauses, which are
complete sentences on their own. Adversative compound sentences contain
two ideas that contrast each other in meaning. The conjunctions used in
such sentences include but, yet, still and so on.
Option B uses the adversative conjunction, 'whereas' which refers to the contrasting ideas: loving "horror movies" and loving "romantic comedies". Hence option B is correct.
Option A uses the adversative conjunction 'yet', which does not bring out the relation between the sentences. 'Yet' means 'in spite of', but the given sentences do not convey the same meaning. Hence A is incorrect.
Option C uses the illative conjunction 'for', which is used in inference-related sentences. The second clause is not inferred from the other. Hence C is incorrect.
Option D is incorrect because the answer lies in B.