The correct answer is B. Not an opinion
Step-by-step explanation:
An opinion is a statement that expresses one's feelings, perspectives or position towards a subject, because of this opinions are subjective and vary in each person, an example of this is the opinion people have about a particular movie. Additionally, the oppositive to an opinion is a fact that does not depend on the thoughts of each person but describes reality and therefore can be proved such as the distance from one place to another. In the case of "The song switches time signatures twice" this is not an opinion because the number of times there are switches in time signatures in a song does not depend on the point of view of people but is a reality that can be proved either by listening to the song or looking at the music sheet.