The correct answer is a compound sentence. A compound sentence is when there are two parts of a sentence that can work alone as complete sentences, but which are combined into one sentence with the use of a conjunction (and, but, etc.). In this case, "I watched the movie" and "I didn't like it" can stand on their own as separate sentences. However, they are conjoined into one sentence by the word "but," a conjunction, which classifies this sentence as compound.