Which sentence states a fact?

 - Building the Great Wall of China took too long.
 - It took hundreds of years to build the Great Wall of China.
The first sentence states a fact.
It took hundreds of years to build the Great Wall of China.
It can be proved by reading about the creation of the Great Wall.
The second sentence states an opinion.
Building the Great Wall of China took too long.
Too long shows what a person believes, thinks, or feels. Another person might have a different opinion about how long is too long.