Which sentence states a fact?
Ennio Morricone composed the music for the 1969 spaghetti western Once Upon a Time in the West. The 1969 spaghetti western Once Upon a Time in the West is director Sergio Leone's worst movie.
A fact is something that can be proved by research or observation.
Napoleon Bonaparte was shorter than King Louis XVI.
The statement above is a fact. The statement can be proved by researching the height of each man and comparing them.
An opinion is something that a person believes, thinks, or feels. An opinion cannot be proved.
Napoleon Bonaparte was a better leader than King Louis XVI.
The statement above is an opinion. People can have different ideas about what makes someone a "better" leader, so the statement cannot be proved.
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.