Which sentence states a fact?

 - Volcanoes are openings in the Earth's rocky crust.
 - Science classes spend too much time covering volcanoes.
The first sentence states a fact.
Volcanoes are openings in the Earth's rocky crust.
It can be proved by reading a book about volcanoes.
The second sentence states an opinion.
Science classes spend too much time covering volcanoes.
Too much time shows what a person believes, thinks, or feels. Another person might have a different opinion about how much time is too much.