Which sentence states a fact?

 - Brazil's flag is green with a yellow diamond and a blue circle.
 - The design of Brazil's flag reflects a lack of imagination.
The second sentence states a fact.
Brazil's flag is green with a yellow diamond and a blue circle.
It can be proved by looking at a Brazilian flag.
The first sentence states an opinion.
The design of Brazil's flag reflects a lack of imagination.
Lack of imagination shows what a person believes, thinks, or feels. Another person might have a different opinion about how imaginative the design is.