Which sentence states a fact?
A: Alexander Graham Bell invented the electric telephone in the 1870s.
B: The telephone was the greatest invention of its time.
The first sentence states a fact.
Alexander Graham Bell invented the electric telephone in the 1870 s.
It can be proved by reading a book about Alexander Graham Bell.
The second sentence states an opinion.
The telephone was the greatest invention of its time.
Greatest shows what a person believes, thinks, or feels. Another person might have a different opinion about what the greatest invention was.