Answer:
The following sentence “I watched the movie last night, but I didn't like it,” is a compound sentence. (Option B)
Explanation:
This kind of a sentence is always formed with two separate sentences that have a complete meaning and are joined with a conjunction. Here, in this sentence, there are two separate sentences namely - “I watched the movie last night” and “I didn't like it.” Both are complete and independent sentences. They also have a proper meaning. These two are joined to form one sentence using a coordinating conjunction “but.”