Which sentence states a fact?
A: Ennio Morricone composed the music for the 1969 spaghetti western Once Upon a Time in the West.
B: The 1969 spaghetti western Once Upon a Time in the West is director Sergio Leone's worst movie.
The second sentence states a fact.
Ennio Morricone composed the music for the 1969 spaghetti western Once Upon a Time in the West.
It can be proved by looking up information about Ennio Morricone in a movie database.
The first sentence states an opinion.
The 1969 spaghetti western Once Upon a Time in the West is director Sergio Leone's worst movie.
Worst shows what a person believes, thinks, or feels. Another person might have a different opinion about which movie is a director's best or worst.